RFR: 8343493: Perform module checks during MetaspaceShared::map_archives()

[Ioi Lam]

Currently, `Modules::serialize()` and `Modules::serialize_addmods_names()` store/retrieve the main module name, as well as the set of modules specified by `--add-modules`. These functions are called from `MetaspaceShared::serialize()`, *after* the JVM has decided to use the CDS archive.

However, with JEP 483 ([JDK-8315737](https://bugs.openjdk.org/browse/JDK-8315737)), we need the module information *before* deciding whether to use the CDS archive. For example, if `-XX:+AOTClassLinking` is specified during the CDS archive creation, the archive cannot be used if we specified an incompatible main module at runtime.

This RFE added a new function, `MetaspaceShared::early_serialize()`, which is called from `MetaspaceShared::map_archives()`. `Modules::serialize()` and `Modules::serialize_addmods_names()` are called within this context so that we can use the module information to decide whether to use the CDS archive or not.

I also added some comments about what "serialize" does, since it's rather non-obvious.

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Commit messages:
 - 8343493: Perform module checks during MetaspaceShared::map_archives()

Changes: https://git.openjdk.org/jdk/pull/21890/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21890&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8343493
  Stats: 89 lines in 6 files changed: 74 ins; 6 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/21890.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21890/head:pull/21890

PR: https://git.openjdk.org/jdk/pull/21890