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It is a bit hard to tell what somebody knows and I got mixed impressions from your first and your later posts.
Anyway:
The build.gradle and the bnd.bnd file snippets contain the important parts. I will reply to the other posts too, but here's my recommendation:
1) You probably already have a Liferay workspace, if not, create one. I believe, the snipped depends on a workspace to be able to resolve all dependencies.
2) Create an Activator sample project
3) Rename it, delete the sourcecode and clean the avtivator line(s) from the bnd.bnd file.
4) Add the build.gradle snippet I posted above to the build.gradle (you probably need to fix/replace the dependencies part depending on your Liferay version.
I hope, it builds then.

The bnd.bnd file is rather irrelevant for the build.
The build.gradle is relevant, itcontains the dependencies and defines the build process. The bnd.bnd file is picked up later on and overrides the bnd file generated by the build. Problems in that file hit you at deployment or maybe later on. (Note: That's not a 100% true, since Liferay picks up things like Bundle-Name but as a rule of thumb, it's correct)
The error tells you that the gradle build doesn't know where to download the dependencies. They are usually defined in the workspace. If you don't have a workspace, you need to add your own list of repositories:
e.g.:

repositories {
  mavenLocal()
  mavenCentral()
}

hth

Ah, I was unclear.
NOT:
buildscript {
    repositories {
...
   }
}
BUT:
buildscript {
    repositories {
...
   }
}

repositories {

mavenLocal()

mavenCentral()

}
--------
Could you please try that?

I am not sure where that class comes from? Is it generated? Or did you write it?
In any case, you can make it compile by adding the dependency:
dependencies {
...
compileOnly group: "junit", name: "junit", version: "4.12"
}
Whether you solve it with an activator sample or "standalone" doesn't matter. In general, for a Liferay project you just need a build.gradle, a bnd.bnd file and source code. That's all. You can write all of it by hand or use a sample and remove the stuff you don't need. For the first few projects it's probably a bit complicated but you will soon know how such a build works.
Once the module builds and deploys successfully, you can start using it.
A note about the dependencies:
compileOnly group: "com.liferay.portal", name: "com.liferay.portal.kernel", version: "4.0.0"
The major version here needs to match your Liferay version. 4.x is Liferay 7.2
https://mvnrepository.com/artifact/com.liferay.portal/com.liferay.portal.kernel
You don't need the exact version, but the major version (here 4) needs to be correct. Otherwise your module won't deploy. Come to think of it: For your generated wsdl code you probably don't even need a dependency to the kernel, so you can probably just remove the dependency. (I hope, I am not confusing you here with too much information)

You probably still don't have a Liferay workspace. I guess, you have created a new standalone gradle project, yes?
I am still a bit confused here about your knowledge. Your first post shows that you have quite some knowledge but the problems you face are quite, well, weird.  My impression is that you have never created a Liferay 7+ project before.
About your requirements, I am not sure we are on the same page  and I need to clarify a few things:
"Produces a complete, working JAXWS/SOAP/CXF web service (e.g. module jar file) that can be deployed in Liferay 7 Portal (both Client and Server)
"When deployed, it can be verified as working (i.e. It shows up in the Liferay Control Panel and can be accessed via URL)."
My example config produces a client, not a server. It generates a library which can be used to access a remote webservice. It's a quite common usecase to do that. I can help you with that and even wipe up a quick, working example if you need it.

But the server is a wholly different story!!
Usually people use tools to create the wsdl from some Java/C#/... API. I actually have never seen it the other way round, except for mocking purposes, e.g. with SoupUI, where you mock the true wsdl backend. Do you really want to do that?
I believe, it is really uncommon to do that, if you need it, fine. But I hope you understand that wsdl2java also creates only the interfaces to start the implementation of the webservice. It creates some basic types, but the result is just an empty shell. Is that clear to you and what you intend?
It can NEVER show up in the control panel, since you would need to implement the methods and configure the Liferay integration yourself.

So, do you need a client and/or a server? Is it clear to you that the server code will have to be implemented by you, that only interfaces are generated?

It was never my intention to imply that you are an idiot. I am sorry that you feel that way. I also apologize if my tone felt arrogant or condescending. Since I feel that I can't help you, there is too much of a communication gap, I believe it's best if I drop out of this conversation.
One last advise:
Maybe open a new thread, people tend to ignore threads with many answers, too much to read to get up to speed.

In any case, since I obviously am unable to explain what has to be done, I have created a working client example. I have attached a workspace with a ws-client module (I took my own advise, created an activator module and changed the build.gradle & bnd.bnd). I have also added a rest example module, it is just there to show how the client is included in the build.gradle and executed.
You should be able to deploy the modules on 7.2. The rest example won't work in 7.0 (maybe it will work in 7.1, but I am doubtful), the ws-client should work in all 7.x versions.
http://localhost:8080/o/greetings
http://localhost:8080/o/greetings/callSoap
I wish you best of luck with the server part, I have never used wsdl2java to create a server, I hope somebody else has some experience with that and can help you.