RFR: 8369449: Spec: introduce new JVMTI function GetTotalGCCpuTime

[Serguei Spitsyn]

With [JDK-8359110](https://bugs.openjdk.org/browse/JDK-8359110) a framework to measure GC CPU time was introduced.
It will be exposed in JMX as `MemoryMXBean.getTotalGcCpuTime()`. There is also interest to get the same performance data from JVMTI.
The following API's are being added with this enhancement:

Introduce:
 - new capability: `can_get_gc_cpu_time`
 - new JVMTI functions:
    - `jvmtiError GetGCCpuTimerInfo(jvmtiEnv* env, jvmtiTimerInfo* info_ptr)`
    - `jvmtiError GetTotalGCCpuTime(jvmtiEnv* env, jlong* nanos_ptr)`

The related CSR will be created shortly.

Testing:
 - TBD: Mach5 tiers 1-6

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Commit messages:
 - 8369449: Spec: introduce new JVMTI function GetTotalGCCpuTime

Changes: https://git.openjdk.org/jdk/pull/27879/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27879&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8369449
  Stats: 102 lines in 4 files changed: 101 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/27879.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27879/head:pull/27879

PR: https://git.openjdk.org/jdk/pull/27879