[jdk13u-dev] RFR: 8255625: AArch64: Implement Base64.encodeBlock accelerator/intrinsic

[Sergey Nazarkin]

I'd like to backport JDK-8257414 to jdk13u for performance improvement. The patch is not applied cleanly due to miss of JDK-8224974. The following block need to be applied manually
    if (UseBASE64Intrinsics) {
        StubRoutines::_base64_encodeBlock = generate_base64_encodeBlock();
    }

Passed tier1 and verify performance change with new test.

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

Commit messages:
 - Backport 8638cd9acf5c33612eaf82ae3219f68456ea9621

Changes: https://git.openjdk.java.net/jdk13u-dev/pull/149/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk13u-dev&pr=149&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8255625
  Stats: 226 lines in 3 files changed: 226 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk13u-dev/pull/149.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk13u-dev pull/149/head:pull/149

PR: https://git.openjdk.java.net/jdk13u-dev/pull/149