Describe the PR

Update the property framework for PMD 7.

• remove deprecated API
• turn PropertyDescriptor into a class because it only needs a single implementation now
• prepare the framework to support new XML syntax in the future. This PR does not change the XML schema, but changes its interpretation in the following places:
  • the delimiter attribute for property definitions is deprecated, produces a warning and its value is ignored.
  • the min and max attributes for property definitions of numeric properties are no longer required, and can now appear separately, or not at all.

Maybe the most arbitrary change is that I removed the ability to configure the delimiter for multi-value properties, and changed the default delimiter to a comma (,) for all properties. The default delimiter was previously inconsistent as string properties used | for some reason. Many properties were overwriting this with a comma, in an inconsistent and unpredictable manner. There is no change in expressivity as the comma may now be escaped by a backslash. The actual reason I did this is because having a custom delimiter complicates the round-tripping through RulesetWriter a lot. Also I expect that the new syntax for list properties (which is not in this PR) will anyway become a nicer way to write list properties when writing a comma-delimited list is ugly.

The API for rules (PropertyFactory) is unchanged except for a couple of new convenience methods, to create enumerated properties from an Enum class.
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Related issues

• Fixes [core] Implementation plan for property framework changes #1432
• Fixes [core] Allow numeric properties in XML to be within an unbounded range #1204
• fix [core] Migrate Property Framework API to Java 8 #4302
• fix [core] Remove deprecated property concrete classes #4301
• fix [doc] Document new property framework #4303
• relates to [core] New property syntax in XML #4305: this does not implement any new syntax, but sets up infrastructure to add this later without breaking everything. We should revert 84cba78.

Ready?

• Review that not too many unit tests are missing
• Review doc pages -> API didn't really change so probably little to do. Ref [doc] Document new property framework #4303
• Add tests for [core] Allow numeric properties in XML to be within an unbounded range #1204
• Release notes
• 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)