RFR: 8331264: Reduce java.lang.constant initialization overhead [v2]

[Claes Redestad]

> I'm looking at ways at reducing/eliminating startup overheads the classfile API in preparation of #17108, and have pushed a series of enhancements to that effect already. This PR is a collection of minor improvements which add up to a 1.5% reduction in retired instructions - or a 5% reduction in executed bytecode - on a simple lambda startup test.

Claes Redestad has updated the pull request incrementally with one additional commit since the last revision:

  Descriptors can't be empty, optimize isArray and isClassOrInterface with descriptorString().charAt(0) ==

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Changes:
  - all: https://git.openjdk.org/jdk/pull/18991/files
  - new: https://git.openjdk.org/jdk/pull/18991/files/c27d5ff8..7e7386e1

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=18991&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=18991&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/18991.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18991/head:pull/18991

PR: https://git.openjdk.org/jdk/pull/18991