RFR: JDK-8250766: javadoc adds redundant spaces when @see program element is wrapped

[Hannes Wallnöfer]

This changes reference parsing in `DocCommentParser` to normalize whitespace in signatures to a large extent. In particular, multiple whitespace characters are coalesced into a single space character, and whitespace after opening parentheses and angle brackets are suppressed.

-------------

Commit messages:
 - JDK-8250766: javadoc adds redundant spaces when @see program element is wrapped

Changes: https://git.openjdk.java.net/jdk/pull/3754/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3754&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8250766
  Stats: 24 lines in 3 files changed: 17 ins; 1 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3754.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3754/head:pull/3754

PR: https://git.openjdk.java.net/jdk/pull/3754