RFR: 8302590: Add String.indexOf(int ch, int fromIndex, int toIndex) [v8]

[Raffaello Giulietti]

> Add an `indexOf()` variant allowing to specify both a lower and an upper bound on the search.

Raffaello Giulietti has updated the pull request incrementally with one additional commit since the last revision:

  git commit -m "8302590: Add String.indexOf(int ch, int fromIndex, int toIndex)"
  
  Moved and renamed test file to parent folder

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Changes:
  - all: https://git.openjdk.org/jdk/pull/12600/files
  - new: https://git.openjdk.org/jdk/pull/12600/files/5bc1edb8..7007ec96

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12600&range=07
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12600&range=06-07

  Stats: 426 lines in 2 files changed: 223 ins; 203 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/12600.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12600/head:pull/12600

PR: https://git.openjdk.org/jdk/pull/12600