RFR: 8301120: Cleanup utility classes java.util.Arrays and java.util.Collections [v2]

[Tagir F. Valeev]

> number of minor cleanups could be done in Arrays and Collections utility classes.
> In Arrays:
> - Redundant import jdk.internal.misc.Unsafe;
> - C-style array declaration is used in public static boolean equals(short[] a, short a2[]) (that's the only place in the whole file)
> 
> In Collections:
> - A few obsolete "unchecked" and "rawtypes" suppressions
> - Unnecessary local variable initializer in get() method
> - Raw type can be avoided in a number of casts
> - Explicit type parameters could be omitted or converted to diamonds
> - A couple of javadoc links on private APIs are malformed

Tagir F. Valeev has updated the pull request incrementally with one additional commit since the last revision:

  Revert cast removal

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/12207/files
  - new: https://git.openjdk.org/jdk/pull/12207/files/f1345d33..ec7b2afc

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12207&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12207&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/12207.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12207/head:pull/12207

PR: https://git.openjdk.org/jdk/pull/12207