RFR: 8320206: Some intrinsics/stubs missing vzeroupper on x86_64

[Sandhya Viswanathan]

The following intrinsics/stubs are missing vzeroupper:
adler32 (since JDK17)
count_positives (since JDK 9)
chacha20 (since JDK 20)
string indexOfChar (since JDK 9)

Adding the missing vzeroupper to avoid AVX-SSE transition penalties.

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Commit messages:
 - add vzeroupper

Changes: https://git.openjdk.org/jdk/pull/16678/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16678&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8320206
  Stats: 7 lines in 3 files changed: 7 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/16678.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16678/head:pull/16678

PR: https://git.openjdk.org/jdk/pull/16678