Upgraded gradle build config to use KTS and misc improvements

[kalmanbencze]

Changes:

• using libs.versions.toml file for declaration of library versions
• rewrote build.gradle -> build.gradle.kts with necessary modernization
• rewrote the buildSrc contents/ renamed to build-logic to define convention plugins
• Rewrote the groovy FilamentPlugin.kt in kotlin
• upgraded gradle to gradle-8.14.3
• tested the plugin to convert the resources + samples to verify them
• updated workflows to run on jvm 21

Testing

• regenerated all resources with the rewritten plugin
• tested all samples
• published the libraries to local maven to make sure the publishing works as before

[kalmanbencze]

hey @ThomasGorisse @grassydragon, I got one more change here to modernise the repo a bit. Let me know if I should try and break it into more pieces, although the groovy to kts gradle dsl change would be hard to do one by one