Use `gradle-buildconfig-plugin` to generate dependency versions

[Goooler]

Generate build config for the versions like

https://github.com/diffplug/spotless/blame/a0ac60042bb4470f9dd7992e11541ca37d025f75/lib/build.gradle#L99

And refer to the generated config for

https://github.com/diffplug/spotless/blob/8d4cd28cb1ed3f2ebfd0e48cc8e5715ef65d6440/lib/src/main/java/com/diffplug/spotless/java/GoogleJavaFormatStep.java#L124

There is an example like https://github.com/vanniktech/gradle-maven-publish-plugin/blob/d0e50fec7a07ef91fde62ae5cb0e4b4b4769d797/plugin/build.gradle.kts#L35-L110

This should be stacked on #2704.

[nedtwigg]

I'm not familiar with this, but I'm open to it. What is the problem that it solves?

[Goooler]

@renovate-bot send the updates like #2345, we have to update GoogleJavaFormatStep.java manually to reflect the latest version string. If we apply the build config stuff, the latest version in the lib will always be refed by

.add(17, BuildConfig.VERSION_GJF); // default version 

and BuildConfig.VERSION_GJF always reflects the latest version bumped by @renovate-bot.

[nedtwigg]

Wow! Great idea, I like it!