RFR: 8258015: [JVMCI] JVMCI_lock shouldn't be held while initializing box classes for AOT [v2]

[Doug Simon]

> This PR fixes a regression caused by JDK-8257917 by not locking JVMCI_lock when initializing the boxing cache classes for AOT.
> 
> It also reduces the calls to `JVMCI::ensure_box_caches_initialized` to be at most one per JVMCI code installation.

Doug Simon has updated the pull request incrementally with one additional commit since the last revision:

  do not synchronize ensure_box_caches_initialized

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1730/files
  - new: https://git.openjdk.java.net/jdk/pull/1730/files/9642d945..91571c1b

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1730&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1730&range=00-01

  Stats: 9 lines in 4 files changed: 2 ins; 3 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1730.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1730/head:pull/1730

PR: https://git.openjdk.java.net/jdk/pull/1730