RFR: 8303648: Add String.indexOf(String str, int beginIndex, int endIndex) [v2]

[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)
  
  Moved @apiNote on indexOf(String,int) before @param/@return.
  Rephrased first sentence of indexOf(String,int,int).

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Changes:
  - all: https://git.openjdk.org/jdk/pull/12903/files
  - new: https://git.openjdk.org/jdk/pull/12903/files/dc4cd3f3..5303bea0

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12903&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12903&range=00-01

  Stats: 12 lines in 1 file changed: 6 ins; 5 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