RFR: 8303648: Add String.indexOf(String str, int beginIndex, int endIndex) [v3]

[Raffaello Giulietti]

> As a followup of [JDK-8302590](https://bugs.openjdk.org/browse/JDK-8302590), this issue covers the analogous case for a search of a string rather than a character.

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

  8303648: Add String.indexOf(String str, int beginIndex, int endIndex)
  
  English grammar correction.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/12903/files
  - new: https://git.openjdk.org/jdk/pull/12903/files/5303bea0..b644469b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12903&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12903&range=01-02

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/12903.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12903/head:pull/12903

PR: https://git.openjdk.org/jdk/pull/12903