8355204: Consider simplifying type metadata stripping

[cushon]

This change removes support for stripMetadataIfNeeded. After JDK-8355065 there are only two uses of the method:

• Types#directSupertypes, which is specified as preserving type annotations. This change means that type metadata will be preserved for supertypes that appear in source, as well as substituted types for transitive supertypes.
• Trees#getTypeMirror, which doesn't specify whether or not type annotations are preserved.

stripMetadataIfNeeded was added for JDK-8031744. The unconditional stripMetadata was added for JDK-8144580. stripMetadata was substantially reworked to ensure it always stripped annotations in JDK-8042981, which also updated the spec for Types' utility methods to clarify when type annotations were preserved, added a public API for removing annotations from types, and replaced some calls to stripMetadataIfNeeded with stripMetadata because the former didn't strip annotations in some cases where stripping was actually needed.

I think it's worth considering removing stripMetadataIfNeeded. The bookkeeping to keep track of whether or not metadata should be stripped is fragile, and the API use-case can be supported by either preserving metadata or unconditionally stripping it.

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Issue

• JDK-8355204: Consider simplifying type metadata stripping (Enhancement - P4)

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[vicente-romero-oracle]

/csr

[openjdk]

@vicente-romero-oracle has indicated that a compatibility and specification (CSR) request is needed for this pull request.

@cushon please create a CSR request for issue JDK-8355204 with the correct fix version. This pull request cannot be integrated until the CSR request is approved.