RFR: 7903841: apidiff: IllegalStateException for RECORD in TypePageReporter

[Jonathan Gibbons]

Please review a trivial fix to include RECORD in the set of known element kinds for classes and interfaces

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Commit messages:
 - CODETOOLS-7903841: apidiff: IllegalStateException for RECORD in TypePageReporter

Changes: https://git.openjdk.org/apidiff/pull/15/files
  Webrev: https://webrevs.openjdk.org/?repo=apidiff&pr=15&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903841
  Stats: 3 lines in 1 file changed: 2 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/apidiff/pull/15.diff
  Fetch: git fetch https://git.openjdk.org/apidiff.git pull/15/head:pull/15

PR: https://git.openjdk.org/apidiff/pull/15