RFR: 8278241: Implement JVM SpinPause on linux-aarch64

[Evgeny Astigeevich]

This JVM SpinPause can use different implementations of spin pauses. It uses `SpinWait` description which is defined with `OnSpinWaitInst`/`OnSpinWaitInstCount` options.  The `SpinWait` provides an instruction runner together with the description of the instruction and the instruction count. It can be used at places where generation of spin pauses is not possible, like in runtime SpinPause function.

The `SpinWait` description is also used for the `_onSpinWait()` intrinsic. We don't have use cases when we need different implementations for the `_onSpinWait()` intrinsic and JVM SpinPause. However JVM SpinPause might need less instructions than the intrinsic. To support such cases the instruction runner interface supports the `count` parameter.

Testing results for fastdebug and release builds:
- `gtest`: Passed
- `tier1`...`tier4`: Passed
- `hotspot/jtreg/runtime/Thread/TestSpinPause.java`: Passed

JVM SpinPause is used for the synchronised statements and can benchmarked with `org.openjdk.bench.vm.lang.LockUnlock.testContendedLock`.

Benchmarking results (number of samples per an experiment: 150) for Graviton2 (Neoverse N1), 1 ISB instruction:



+-----------+-------------------+------------+-----------+-----------+----------+---------+
| CPU cores | Contended threads | Base ns/op |   Error   |    New    |  Error   |  Diff   |
+-----------+-------------------+------------+-----------+-----------+----------+---------+
|         8 |                64 |  10007.213 | ±910.911  |  8527.346 | ±377.242 | -14.79% |
|        16 |                64 |  10274.935 | ±880.568  |  8310.433 | ±326.845 | -19.12% |
|        32 |                64 |  12231.947 | ±1525.364 |  9205.941 | ±394.409 | -24.74% |
|        64 |                64 |    9929.49 | ±586.074  | 10488.695 | ±570.458 | 5.63%   |
|        64 |                32 |   5605.119 | ±629.340  |  5023.882 | ±230.639 | -10.37% |
|        64 |                16 |   2817.346 | ±263.696  |  2367.528 | ±94.158  | -15.97% |
|        64 |                 2 |    870.389 | ±530.579  |   464.395 | ±126.260 | -46.65% |
+-----------+-------------------+------------+-----------+-----------+----------+---------+

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Commit messages:
 - 8278241: Implement JVM SpinPause on linux-aarch64

Changes: https://git.openjdk.java.net/jdk/pull/6803/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6803&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8278241
  Stats: 138 lines in 5 files changed: 130 ins; 0 del; 8 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6803.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6803/head:pull/6803

PR: https://git.openjdk.java.net/jdk/pull/6803