Add SpringBootTransformer for merging Spring Boot configuration files

[Copilot]

Spring Boot resource files (e.g., spring.factories, *.imports) are silently overwritten when multiple JARs are combined into a shadow JAR, breaking auto-configuration discovery. This adds a dedicated SpringBootTransformer that merges these files correctly.

Changes

• New SpringBootTransformer extends PatternFilterableResourceTransformer (same pattern as ServiceFileTransformer) and handles the following resource files:
  • META-INF/spring.factories — comma-separated class lists; merged by appending values per key
  • META-INF/spring.handlers / spring.schemas / spring.tooling / spring-autoconfigure-metadata.properties — merged the same way
  • META-INF/spring/*.imports (Spring Boot 3+) — deduplicated line-per-class merge
• Relocation-aware: dot-notation values (class names) use relocateClass; slash-notation values (resource paths, e.g. in spring.schemas) use relocatePath
• @CacheableTransformer annotated; state tracked via @Internal maps
• Default PatternSet covers all Spring Boot resource paths; users can customize includes/excludes via the inherited PatternFilterable API

Usage

tasks.shadowJar {
    transform(SpringBootTransformer::class.java)
    // optionally with relocation
    relocate("com.example", "shadow.example")
}

• CHANGELOG's "Unreleased" section has been updated, if applicable.

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[Goooler]

@copilot Simplify this by PatternFilterableResourceTransformer

[Copilot]

@copilot Simplify this by PatternFilterableResourceTransformer

Done in 259d7d0. SpringBootTransformer now extends PatternFilterableResourceTransformer with a default PatternSet (like ServiceFileTransformer), removing the @Inject/ObjectFactory constructor, the canTransformResource() override, and the internal PROPERTIES_PATHS set.

[Goooler]

It's so complex. I'll leave it closed for now.

[Goooler]

Merged into #2093.