Integral refactor: Gradle 8, Android support, minor DSL changs and behavior

[gmazzo]

• Gradle 8 support
• CI moved to GHA
• Updated demos honoring Configuration avoidance
• Android support (fixes How to configure it in android modules? #34 and Make the generated BuildConfig recognizable by the IDE #36)

Breaking changes:

• Minimum JDK is now 11
• Kotlin generator now uses internal visibility by default
• Multiple BuildConfigTask of the same SourceSet now are merged into a single one:
  • className, packageName and generator now can only be customized by SourceSet and no per-class anymore
  • packageName and generator for secondary SourceSets defaults to the main one

[codecov]

Codecov Report

Merging #40 (382dac8) into main (6955c74) will decrease coverage by 6.38%.
The diff coverage is 80.80%.

@@             Coverage Diff              @@
##               main      #40      +/-   ##
============================================
- Coverage     86.89%   80.51%   -6.38%     
+ Complexity       75       54      -21     
============================================
  Files            18       15       -3     
  Lines           267      231      -36     
  Branches         12       17       +5     
============================================
- Hits            232      186      -46     
- Misses           24       32       +8     
- Partials         11       13       +2     

Impacted Files	Coverage Δ
...thub/gmazzo/gradle/plugins/BuildConfigClassSpec.kt	33.33% <ø> (-4.17%)	⬇️
...thub/gmazzo/gradle/plugins/BuildConfigSourceSet.kt	16.66% <0.00%> (-23.34%)	⬇️
...ns/internal/bindings/KotlinMultiplatformHandler.kt	0.00% <ø> (ø)
...dle/plugins/generators/BuildConfigJavaGenerator.kt	93.54% <66.66%> (ø)
...om/github/gmazzo/gradle/plugins/BuildConfigTask.kt	80.95% <75.00%> (-15.60%)	⬇️
...e/plugins/generators/BuildConfigKotlinGenerator.kt	87.87% <83.33%> (ø)
...le/plugins/internal/DefaultBuildConfigClassSpec.kt	90.00% <87.50%> (-4.12%)	⬇️
.../github/gmazzo/gradle/plugins/BuildConfigPlugin.kt	87.09% <89.47%> (-8.68%)	⬇️
...le/plugins/internal/DefaultBuildConfigSourceSet.kt	92.85% <92.85%> (+7.14%)	⬆️
...e/plugins/internal/BuildConfigSourceSetInternal.kt	100.00% <100.00%> (ø)
... and 2 more

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more