RFR: 8339640: Reduce construction overheads in StringConcatFactory$InlineHiddenClassStrategy [v2]

[Claes Redestad]

> Using the trusted `invokeBasic` method streamlines invokers and avoids spinning up of some type conversion handles. This reduces classes generated in a few scalability stress tests.

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

  Explicitly cast to Object

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Changes:
  - all: https://git.openjdk.org/jdk/pull/20884/files
  - new: https://git.openjdk.org/jdk/pull/20884/files/c53f99f7..8bf73809

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20884&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20884&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/20884.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20884/head:pull/20884

PR: https://git.openjdk.org/jdk/pull/20884