RFR: 8265605: Cannot call BootLoader::loadClassOrNull before initPhase2 [v2]

[Ioi Lam]

> This bug was discovered during the development of [JDK-6824466](https://bugs.openjdk.java.net/browse/JDK-6824466): when CDS is enabled, if `BootLoader::loadClassOrNull` is called before `initPhase2`, it would trigger the initialization of the archived module graph in the wrong order. Because of unanticipated nesting of `<clinit>` methods, `BootLoader::SERVICES_CATALOG` becomes empty, causing future `ServiceLoader` operations to fail.
> 
> The fix has 2 parts:
> 
> - `BootLoader::loadClassOrNull` no longer calls `ClassLoaders::bootLoader()`. This avoids triggering the archived module graph initialization. Instead, it makes a direct call to `Classloader::findBootstrapClassOrNull()`. We don't actually need a `ClassLoader` instance for this call, so I changed `Classloader::findBootstrapClassOrNull()` to be a static method.
> - The object returned by `BootLoader::getServicesCatalog()` is now maintained inside `jdk.internal.loader.ClassLoaders`.  Although not strictly required for the fix, this simplifies the initialization of the archived module graph. It also makes the logic consistent for the 3 built-in loaders (boot/platform/app).
> 
> Testing: tiers1-4 in progress. I also verified that the bug reported by Mandy is no longer reproducible after I applied this patch on her branch.

Ioi Lam has updated the pull request incrementally with one additional commit since the last revision:

  @AlanBateman comments

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/3992/files
  - new: https://git.openjdk.java.net/jdk/pull/3992/files/ebaa6614..8067306a

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=3992&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=3992&range=00-01

  Stats: 8 lines in 2 files changed: 5 ins; 2 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3992.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3992/head:pull/3992

PR: https://git.openjdk.java.net/jdk/pull/3992