RFR: 8175874: Security.insertProviderAt should throw IllegalArgumentException when index is illegal

[Ben Perez]

Fixing the bug as stated would cause compatibility issues. E.g. the `addProvider` function always adds new providers at position 0 and therefore would always throw an error. Instead of changing how the function handles indices, we instead have left an `@implNote`

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Commit messages:
 - removed unnecessary newlines
 - added impl note to insertProviderAt

Changes: https://git.openjdk.org/jdk/pull/14925/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14925&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8175874
  Stats: 4 lines in 1 file changed: 4 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/14925.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14925/head:pull/14925

PR: https://git.openjdk.org/jdk/pull/14925