RFR: 8297530: java.lang.IllegalArgumentException: Negative length on strings concatenation [v2]

[Claes Redestad]

> When concatenating Strings, OutOfMemoryError should be thrown on all overflow conditions. This fixes a case that erroneously thro IAE on concatenations of long (`length > Integer.MAX_VALUE/2`) UTF16 strings due failing to check for overflow after shifting index left with the coder.
> 
> This was caught by a fuzzer test. Added a sanity test that fails without the patch (loosely derived from ImplicitStringConcatMany.java)

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

  Require 64-bit arch to avoid (most) hypothetical false positives

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Changes:
  - all: https://git.openjdk.org/jdk/pull/11354/files
  - new: https://git.openjdk.org/jdk/pull/11354/files/884dac30..124a7350

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11354&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11354&range=00-01

  Stats: 3 lines in 1 file changed: 0 ins; 2 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/11354.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11354/head:pull/11354

PR: https://git.openjdk.org/jdk/pull/11354