[lworld] RFR: 8294927: [lworld] LambdaMetafactory class should reject identity and value superinterface

[Mandy Chung]

This PR adds the validation in LambdaMetafactory to reject if the return type of the given factory type is not an identity interface and not a value interface.   This also fixes a bug in `Class::isIdentity` to return false for interfaces if Valhalla is not enabled.

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Commit messages:
 - Fix Class::isIdentity to return false for interfaces if Valhalla is disabled
 - Merge branch 'lworld' of https://github.com/openjdk/valhalla into lmf-validate
 - 8294927: [lworld] LambdaMetafactory class should reject identity and value superinterface

Changes: https://git.openjdk.org/valhalla/pull/783/files
 Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=783&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8294927
  Stats: 258 lines in 11 files changed: 251 ins; 0 del; 7 mod
  Patch: https://git.openjdk.org/valhalla/pull/783.diff
  Fetch: git fetch https://git.openjdk.org/valhalla pull/783/head:pull/783

PR: https://git.openjdk.org/valhalla/pull/783