[jdk17u] RFR: 8269280: (bf) Replace StringBuffer in *Buffer.toString()

[Aleksey Shipilev]

Clean backport to improve performance in post-BiasedLocking world.

Additional testing: 
 - [x] `java/nio/Buffer` tests are passing
 - [x] Re-generating the test code from the new template yields the same contents

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Commit messages:
 - Backport 3a8f3d6cac0ab859704db533bf1f63431fbd9253

Changes: https://git.openjdk.java.net/jdk17u/pull/35/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk17u&pr=35&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8269280
  Stats: 654 lines in 9 files changed: 638 ins; 5 del; 11 mod
  Patch: https://git.openjdk.java.net/jdk17u/pull/35.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk17u pull/35/head:pull/35

PR: https://git.openjdk.java.net/jdk17u/pull/35