RFR: 8262807: Note assumptions of core reflection modeling and parameter handling

[Joe Darcy]

Please review the javadoc change below, written in response to recent discussion on core-libs.

The bulk of the change is to add a discussion to java.lang.reflect's package-info file about a language vs JVM model for core reflection. That discussion is then linked to from several relevant locations core reflection. A discussion of generic parameter handling is also added along with various small cleanups.

I'll update copyright, etc. after agreement on the text is reached.

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Commit messages:
 - Appease jcheck.
 - 8262807: Note assumptions of core reflection modeling and parameter handling

Changes: https://git.openjdk.java.net/jdk/pull/3036/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3036&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8262807
  Stats: 90 lines in 4 files changed: 69 ins; 6 del; 15 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3036.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3036/head:pull/3036

PR: https://git.openjdk.java.net/jdk/pull/3036