RFR: JDK-8276653: Missing row headers in j.l.Character docs

[Ludvig Janiuk]

The first table is missing row headers, adding them to aid screen readers.

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Commit messages:
 - Added row headers in Character docs

Changes: https://git.openjdk.java.net/jdk/pull/6262/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6262&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8276653
  Stats: 11 lines in 1 file changed: 0 ins; 0 del; 11 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6262.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6262/head:pull/6262

PR: https://git.openjdk.java.net/jdk/pull/6262