[doc] Document rule changes for PMD 7

[adangel]

Related issues

• Fixes [doc] Differences in rules in pmd 7 vs pmd 6 #3123
• Closes [apex] ExcessivePublicCount doesn't consider inner classes correctly #4509
• Closes [java] LocalVariableCouldBeFinal shouldn't report unused variables #4511
• Closes [java] MethodArgumentCouldBeFinal shouldn't report unused parameters #4512
• Closes [java] UselessOperationOnImmutable various false negatives with String #4513
• Closes [java] AvoidLiteralsInIfCondition false positive and negative for String literals when ignoreExpressions=true #4514
• Closes [java] UnusedLocalVariable: false-negative with try-with-resources #4516
• Closes [java] UnusedLocalVariable: false-negative with compound assignments #4517
• Closes [java] UnusedLocalVariable: false-positive with multiple for-loop indices #4518

Ready?

• Added unit tests for fixed bug/feature
• Passing all unit tests
• Complete build ./mvnw clean verify passes (checked automatically by github actions)
• Added (in-code) documentation (if needed)

[pmd-test]

	1 Message
📖	Compared to master: This changeset changes 0 violations, introduces 0 new violations, 0 new errors and 0 new configuration errors, removes 0 violations, 13 errors and 0 configuration errors. Full report
✅	Compared to master: This changeset changes 0 violations, introduces 0 new violations, 0 new errors and 0 new configuration errors, removes 0 violations, 13 errors and 0 configuration errors. Full report
✅	Compared to master: This changeset changes 0 violations, introduces 0 new violations, 0 new errors and 0 new configuration errors, removes 0 violations, 13 errors and 0 configuration errors. Full report
✅	Compared to master: This changeset changes 0 violations, introduces 0 new violations, 0 new errors and 0 new configuration errors, removes 0 violations, 13 errors and 0 configuration errors. Full report
✅	No regression tested rules have been changed.

Generated by 🚫 Danger

[adangel]

So, that's finally ready now.

Most important points:

• changed the property minimum for SwitchDensity from decimal to integer for consistency with the other rules
• The following issues are not resolved and still open, but I could confirm them:
  • [java] CommentRequired doesn't consider annotations and records #4515
  • [java] [7.0-rc1] UnnecessaryImport - Unused static import is being used #4432