RFR: 8261673: Move javadoc for the lookup mechanism to module-info

[Joe Wang]

Consolidate and move javadoc for the lookup mechanism to the module summary.

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

Commit messages:
 - 8261673: Move javadoc for the lookup mechanism to module-info

Changes: https://git.openjdk.java.net/jdk/pull/3020/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3020&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8261673
  Stats: 602 lines in 9 files changed: 197 ins; 361 del; 44 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3020.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3020/head:pull/3020

PR: https://git.openjdk.java.net/jdk/pull/3020