RFR: 8253812: Cleanup AbstractMemberWriter API

[Jonathan Gibbons]

This is primarily a cosmetic cleanup for the doc comments on `AbstractMemberWriter`, but cleaning up some of the
comments leaked into fixing up comments on overridden methods as well.

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Commit messages:
 - Cleanup AbstractMemberWriter API

Changes: https://git.openjdk.java.net/jdk/pull/405/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=405&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8253812
  Stats: 221 lines in 2 files changed: 23 ins; 70 del; 128 mod
  Patch: https://git.openjdk.java.net/jdk/pull/405.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/405/head:pull/405

PR: https://git.openjdk.java.net/jdk/pull/405