Continue refinements of AddSettingsPluginRepository

[shanman190]

What's changed?

• Fixes the AddSettingsPluginRepository recipe to correctly handle pluginManagement block placement in Gradle settings files, and corrects invalid test examples introduced in Fix AddSettingsPluginRepository duplicate pluginManagement when not first statement #7105.

• Insertion of new pluginManagement blocks now skips past any leading import statements before inserting at position 0

• Removed Groovy DSL tests that placed rootProject.name before pluginManagement (invalid in Groovy — "The pluginManagement {} block must appear before any other statements in the script")

• Retained Kotlin DSL "not first statement" tests with rootProject.name before pluginManagement (valid in Kotlin DSL)

• Added noPluginManagementBlockWithBuildCacheKts test covering the customer-reported scenario where buildCache exists and pluginManagement must be inserted before it

What's your motivation?

• PR Fix AddSettingsPluginRepository duplicate pluginManagement when not first statement #7105 fixed duplicate pluginManagement detection but introduced test cases with invalid Gradle scripts and didn't account for the different ordering rules between Groovy and Kotlin DSL.

Verified with Gradle 9.3.1:

• Groovy DSL: pluginManagement must be the absolute first statement (only imports may precede it). buildscript, buildCache, rootProject.name — all fail if placed before it.
• Kotlin DSL: pluginManagement can appear after most blocks (buildCache, rootProject.name, include()), but buildscript cannot appear before it.

Checklist

• I've added unit tests to cover both positive and negative cases
• I've read and applied the recipe conventions and best practices
• I've used the IntelliJ IDEA auto-formatter on affected files

[timtebeek]

Thanks a lot!