initial outline of buildSrc convention plugins

[aSemy]

A quick stab at showing how buildSrc convention plugins can be implemented after I saw your SO post :)

buildSrc convention plugins really help with reducing duplicated Gradle config. Configuration is more standardised and easier to change across a large project.

Subprojects can still override the config set in the plugins if necessary, thus improving legibility so the differences are more pronounced.

Further work:

• [ ] migrate configure-crash-logger.gradle to a buildSrc plugin
• [ ] add the Maven publishing properties (credentials and POM details) to the publishing convention plugin
• [ ] Verify that the published modules are still the same (I've configured a local Maven repo for this - just run ./gradlew publishToLocalProjectDir
• [ ] use the convention plugins in all subprojects
• [ ] tidy up the commented-out code that's been migrated

Also bumps Gradle to 7.5.1