Some gradle build-related updates

[aferg]

• Created version catalog file and migrated plugins, modules, versions to it
• Removed ext block as versions are now defined in version catalog
• Replaced source/target compatibility with toolchain
• Switched a couple of file/dir references to use layout API
• Changing publications to use configurations.configureEach instead of all

[wilkinsona]

Thanks for the suggestions but they're almost all subjective and we prefer not to use version catalogs and toolchains.

[aferg]

No worries at all - figured there was no harm in submitting :)