RFR: 8341295: Add some useful debugging APIs to the debug agent

[Chris Plummer]

The following APIs are useful when debugging the debug agent. Calls to them can be added to the code as needed (temporarily) to aid in debugging issues. They were taken from `test/lib/jdk/test/lib/jvmti/jvmti_common.hpp` and modified to better fit the needs and coding style of the debug agent.

char* translateThreadState(jint flags);
char* getThreadName(jthread thread);
char* getMethodName(jmethodID method);
void printStackTrace(jthread thread);
void printThreadInfo(jthread thread);

I made use of them while working on a couple of recent bugs and found them very useful. 

Tested by running all debugging tests on all supported platforms, and also running tier2, tier3, and tier5 svc ci test tasks.

-------------

Commit messages:
 - Add some useful debugging apis

Changes: https://git.openjdk.org/jdk/pull/21299/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21299&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8341295
  Stats: 188 lines in 2 files changed: 188 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/21299.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21299/head:pull/21299

PR: https://git.openjdk.org/jdk/pull/21299