Tidy up core's build file

[bsideup]

After #4171, we no longer need excludes, so I took a chance to make our build file shorter :)

[lanwen]

Suggested change

	testCompileClasspath 'org.jetbrains:annotations:21.0.1'
	testCompileOnly 'org.jetbrains:annotations:21.0.1'

shouldn't be that with Only suffix? As *Classpath configurations are intended to be resolvable, but not consumable

https://discuss.gradle.org/t/what-is-a-configuration-which-cant-be-directly-resolved/30721

[bsideup]

It was testCompileClasspath before, so I suggest we address it separately, as this PR is something massive already :)

[lanwen]

okay, didn't notice it was moved

[bsideup]

I will try to polish this PR and reduce the changeset while fixing the merge conflict 👍

[bsideup]

Done

[bsideup]

I just found a regression in the generated POM, will fix 👍

[bsideup]

The issue is fixed now (and a check added that verifies that every property of POM dependencies in set (in that case, version was missing due to the usage of platform(...), and changing it to resolvedConfiguration fixed it)

[rnorth]

I think this is looks tidier, so LGTM.

In general, it feels uncomfortable that we have to do so much scripting for all this - I wouldn't claim to understand much of what's going on here or why.

Is there some feedback we should be giving for the Shadow plugin so that they can fill any feature gaps, rather than us?

[bsideup]

@rnorth that was I was planning to do! I do feel like a good amount of this code could be moved to the plugin, and it will be beneficial to many Shadow users 👍

Have submitted #4478 for this