RFR: 8270947: AArch64: C1: use zero_words to initialize all objects

[Andrew Haley]

C1 has its own code generators for zeroing words. We use the same logic for C1 and C2, which should give us better C1 performance and result in less code to maintain.

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Commit messages:
 - Untabify
 - Test
 - Better loops
 - Merge https://git.openjdk.java.net/jdk into c1-initialize
 - comments
 - Benchmark
 - Cleanup
 - Better
 - Intermediate
 - Intermediate
 - ... and 1 more: https://git.openjdk.java.net/jdk/compare/515113d8...5a1acc81

Changes: https://git.openjdk.java.net/jdk/pull/4919/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4919&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8270947
  Stats: 28931 lines in 8 files changed: 28779 ins; 116 del; 36 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4919.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4919/head:pull/4919

PR: https://git.openjdk.java.net/jdk/pull/4919