Expand star imports in ChangePackage and related recipes when they would create ambiguity

[steve-aom-elliott]

Summary

• When ChangePackage renames a star import (e.g., import javax.validation.constraints.* → import jakarta.validation.constraints.*), it now detects if the new package contains types whose simple names clash with types from other star imports (e.g., org.hibernate.validator.constraints.* also has NotBlank)
• If ambiguity is detected, only the changed star import is expanded into explicit imports for the types actually referenced in the source, leaving other star imports untouched
• Uses JavaSourceSet classpath to enumerate types in each package, then walks AST identifiers to determine which types are actually referenced
• ChangeType now also detects when its target type is covered by a star import that would become ambiguous with another star import, and inserts an explicit import to disambiguate
• ChangeDependencyGroupIdAndArtifactId (Maven) and AddDependency (Maven and Gradle) now update the JavaSourceSet marker when changing or adding dependencies, so downstream recipes like ChangePackage and ChangeType have accurate classpath data for ambiguity detection
• JavaSourceSetUpdater.addDependency now tries the project's actual Maven repositories instead of hardcoding Maven Central, fixing failures in air-gapped environments or projects using private repositories
• Shared withSourceTypesOnClasspath test helper extracted to Assertions.java for reuse across test classes

Test plan

• changePackageExpandsStarImportWhenItWouldCreateAmbiguity — uses real javax.validation, jakarta.validation, and org.hibernate.validator types; verifies star import is expanded to explicit imports when another star import contains a type with the same simple name
• changePackagePreservesStarImportWhenNoAmbiguity — verifies star import is preserved when no ambiguity exists
• changeTypeAddsExplicitImportWhenStarImportsWouldBeAmbiguous — verifies ChangeType inserts an explicit import when two star imports would both provide the target type's simple name
• composedWithChangePackageUpdatesImports — end-to-end test composing ChangeDependencyGroupIdAndArtifactId + ChangePackage to verify import renaming works when the JavaSourceSet is updated by the dependency change
• Existing ChangePackageTest, ChangeTypeTest, and ChangeDependencyGroupIdAndArtifactIdTest suites pass

[sambsnyd]

The JavaSourceSet updating functionality within AddDependency , ChangeDependnecy, etc., are all very similar. Perhaps that functionality could be moved into JavaSourceSet itself to simplify and keep standard the recipes which update it

[steve-aom-elliott]

@sambsnyd Ended up squashing most of the previous commits in some form and rebasing the branch again. The changes that I made following your last comment are all part of: a5abf62