StringMap: Generalize equals/hashCode across implementations

[rschmitt]

This change rewrites the equals and hashCode implementations in SortedArrayStringMap and JdkMapAdapterStringMap to support value-based equality between the two implementations.

Fixes #3669.

[github-actions]

Job	Requested goals	Build Tool Version	Build Outcome	Build Scan®
build-windows-latest	clean install	3.9.8	✅

Generated by gradle/develocity-actions

[vy]

Wouldn't it be better to

1. ReadOnlyStringMapUtil internal class such that
   • It contains a static equals(ReadOnlyStringMap,ReadOnlyStringMap) method
   • It contains a hashCode(ReadOnlyStringMap) method
2. Use ReadOnlyStringMapUtil to implement equals and hashCode in all ReadOnlyStringMap implementations

[rschmitt]

@vy OK

[rschmitt]

What should I do about these baseline failures?

[vy]

@rschmitt, bump the @Version tag to 2.25.0 in package-info.java files located where you touched files. (Just answering your question, next week I will review your PR in detail.)

[ppkarwasz]

Thanks everyone for tackling this pull request!

Just to add my perspective: while ReadOnlyStringMapUtil initially seemed like a solid solution, introducing it creates a binary incompatibility between log4j-core 2.25.x and log4j-api 2.24.x. Since the main goal of #3669 is to support unit testing, it might be preferable to avoid that incompatibility and take a simpler—albeit slightly less efficient—approach by using ReadOnlyStringMap.toMap() within the equals() and hashCode() implementations.