RFR: 8317356: Test ClassFile API if it deals with nulls correctly across the whole API

[Chen Liang]

Please review this patch that adds a test by @nizarbenalla to perform null checks across the ClassFile API. This is an updated version of #20556 that minimizes impact on our implementation code.

Notes:
1. There's one change in `MethodHandleProxies` to explicitly use platform class loader instead of `null` for boot class loader. Tests work fine.
2. The null check test uses the same set of classes as CorpusTest to make it suitable for tier 1.
3. The test is not comprehensive; currently it is permissive toward IAE, because sometimes some substitution arguments are invalid, especially primitive ClassDesc or Opcode with wrong types.

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Commit messages:
 - 8317356: Test ClassFile API if it deals with nulls correctly across the whole API

Changes: https://git.openjdk.org/jdk/pull/21458/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21458&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8317356
  Stats: 1202 lines in 38 files changed: 1085 ins; 14 del; 103 mod
  Patch: https://git.openjdk.org/jdk/pull/21458.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21458/head:pull/21458

PR: https://git.openjdk.org/jdk/pull/21458