Adds Spotless with ktlint (Kotlin) and google-java-format (Java) so formatting is checked automatically on pull requests, instead of in review comments.

The configuration matches the one already used in android-maps3d-samples, so all the Maps Android repos format code the same way.

Changes

• build: add Spotless with ktlint...:
  • Spotless 8.9.0 in the version catalog and one root spotless {} block covering every .kt and .java file, including the tutorials outside the Gradle build.
  • Java uses googleJavaFormat().aosp() (4-space), matching the existing code. .editorconfig now has max_line_length = 120 for Kotlin.
  • A ./gradlew spotlessCheck step in the lint job of lint.yml, and a note in CONTRIBUTING.md to run ./gradlew spotlessApply before opening a PR.
• style: apply Spotless formatting: the output of ./gradlew spotlessApply, plus manual, behaviour-neutral fixes ktlint cannot do on its own: wildcard imports replaced, misplaced KDocs turned into block comments, long lines wrapped, and long string literals (mostly @Sample / @SnippetItem descriptions) split with + so their values are unchanged. Seven lines over 120 characters are suppressed instead (raw-string Gemini prompts and one URL).

Disabled ktlint rules, so this stays formatting-only:

• package-name, property-naming, backing-property-naming, filename: fixing them would mean renames.
• annotation-spacing: in several ApiDemos files the // [START ...] tag sits between @Sample(...) and the class, and this rule would move the tag above the annotation, pulling @Sample into the published snippet.

Region tags

Checked against main: every file has the same [START / [END tags in the same order, each still on its own line, and no code moved into or out of a region. Code inside some regions is re-indented or reformatted (for example trailing commas or expression bodies), so the published snippets will look slightly different after the next docs sync.

Merging

Please use rebase and merge so the reformat stays a separate commit. After merging, I will add its SHA to .git-blame-ignore-revs in a small follow-up, so git blame skips it.

Open PRs will likely need a rebase and a ./gradlew spotlessApply after this lands.

Verification

./gradlew spotlessCheck assembleDebug testDebugUnitTest pass locally, and the androidTest sources for snippets:kotlin-app and ApiDemos:kotlin-app compile.