RFR: 8327425: String Template FMT Refactor use call direct instead of MethodHandler

[Shaojin Wen]

Currently FormatItem uses MethodHandler to handle latin1 and utf16, which is not readable. This PR uses direct calls instead of MethodHandler.

Please review and don't hesitate to critique my approach and patch.

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Commit messages:
 - Merge remote-tracking branch 'upstream/master' into refactor_format_item_x
 - Merge remote-tracking branch 'upstream/master' into refactor_format_item_x
 - refactor FormatItem, call directly instead of using MethodHandler

Changes: https://git.openjdk.org/jdk/pull/16021/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16021&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8327425
  Stats: 682 lines in 10 files changed: 344 ins; 245 del; 93 mod
  Patch: https://git.openjdk.org/jdk/pull/16021.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16021/head:pull/16021

PR: https://git.openjdk.org/jdk/pull/16021