RFR: JDK-8283594: Improve docs of ElementScanner classes [v2]

[Joe Darcy]

> Simple update to add links. In the subclasses, the erasure of the parameter's type needs to be used for the link to be recognized as valid.
> 
> After getting reviews, I'll reflow the paragraphs before pushing.

Joe Darcy has updated the pull request incrementally with one additional commit since the last revision:

  Reflow updated paragraphs.

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/7932/files
  - new: https://git.openjdk.java.net/jdk/pull/7932/files/035d7e40..d0b65388

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=7932&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=7932&range=00-01

  Stats: 50 lines in 5 files changed: 8 ins; 0 del; 42 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7932.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7932/head:pull/7932

PR: https://git.openjdk.java.net/jdk/pull/7932