RFR: 8322322: Support archived full module graph when -Xbootclasspath/a is used

[Calvin Cheung]

Please review this change for enabling full module graph even when -Xbootclasspath/a is specified. The validation of -Xbootclasspath/a is already being done in `FileMapInfo::validate_boot_class_paths()`. The full module graph will be disabled if there's a mismatch in -Xbootclasspath/a between dump time and runtime.

The changes in ClassLoaders.java is for setting up the append class path for the boot loader retrieved from the CDS archive. It is required because some existing tests are using the `getResourceAsStream()` api. Those tests would fail without the change.

Passed tiers 1 - 4 testing.

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Commit messages:
 - 8322322: Support archived full module graph when -Xbootclasspath/a is used

Changes: https://git.openjdk.org/jdk/pull/17178/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17178&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8322322
  Stats: 46 lines in 4 files changed: 33 ins; 10 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/17178.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17178/head:pull/17178

PR: https://git.openjdk.org/jdk/pull/17178