RFR: JDK-8306952: improve generic signature of internal DCInlineTag class

[Jonathan Gibbons]

Please review a small update to the generic signature of the internal `DCInlineTag` class, to improve its use in chained method calls.

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Commit messages:
 - JDK-8306952: improve generic signature of internal DCInlineTag class

Changes: https://git.openjdk.org/jdk/pull/13678/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13678&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8306952
  Stats: 11 lines in 1 file changed: 0 ins; 0 del; 11 mod
  Patch: https://git.openjdk.org/jdk/pull/13678.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13678/head:pull/13678

PR: https://git.openjdk.org/jdk/pull/13678