Examples separate projects

[Jolanrensen]

Fixes #1614
Step 3 of #1661

• Introduces example structure like:

  • /examples/projects/1,2,3: release versions of examples
  • /examples/projects/dev/1,2,3: dev versions of examples
    Dev versions of the examples are built using the sources of the project, while release examples use the latest release versions.
    Since any example is a completely separate project, you can attach them to the IDE separately only if you need it :).
    And most importantly, each example could be extracted to a ZIP and runnable by a user without any additional setup (TODO test this)

• Running :promoteExamples copies all /dev examples upwards, making them the new "release" versions. :syncExampleFolders is run afterwards.

• Running :syncExampleFolders (run automatically every :assemble) overwrites all relevant versions and properties in the examples from our main libs.versions.toml, gradle-wrapper.properties, .editorconfig, etc. This also works for any maven examples (see build-logic/src/.../buildExampleProjects for the specific implementaiton)

• Running the Test task :buildExampleFolders (run automatically every :test in debug mode, so on TC) builds all example projects using TestBuildingExampleProjects.

  • Thanks to the :syncExampleFolders task, all dev Gradle Example projects get includeBuild("../../../..") in settings.gradle.kts, which substitutes any DataFrame dependeny with our actual sources. This also makes working inside them from the IDE as easy as if it were a subproject :).
  • The Android examples are ignored if the Gradle property android.sdk.dir is unset. I modified TeamCity to provide -Pandroid.sdk.dir=%env.ANDROID_SDK_HOME% and it seems to work :) This gradle property is passed down to any example containing "android" (in any form) in its name. (This logic can change if needed)
  • The Maven dev project requires a published version of DataFrame. We cannot substitute a Gradle build into Maven in the same way (AFAIK). So for that we use :publishLocal to publish the artifacts to /build/maven before running the tests.