RFR: 8261400: Reflection member filtering registration might be flawed

[Chen Liang]

Please review this patch that address the reflection member filtering flaws.

1. Remove a pointless bootstrap check to ensure no filter is accidentally bypassed due to class-loading order.
2. Clarify the scenarios for filtering, and the correct filter actions for each scenario.
3. Remove the filter in `sun.misc.Unsafe`; users are already using other ways to steal this instance, bypassing the filtered getter. The `jdk.internal.misc.Unsafe`'s filter was already removed in JDK-8161129, so this filter is meaningless.

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Commit messages:
 - Simplify comments
 - Merge branch 'master' of https://github.com/openjdk/jdk into fix/reflection-filter
 - Merge branch 'master' of https://github.com/openjdk/jdk into fix/reflection-filter
 - Minor refinement, future-proof comments
 - 8261400: Reflection member filtering registration might be flawed

Changes: https://git.openjdk.org/jdk/pull/20058/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20058&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8261400
  Stats: 38 lines in 4 files changed: 16 ins; 14 del; 8 mod
  Patch: https://git.openjdk.org/jdk/pull/20058.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20058/head:pull/20058

PR: https://git.openjdk.org/jdk/pull/20058