JFR Optimization - Prevent String duplication

[meiao]

Is your feature request related to a problem? Please describe.

When creating the JvmStackFrames the daemon instantiates a new String for each method in the stacktrace.

This causes duplicates, since there could be other stacktraces with similar methods, and the likely hood of identical stacktraces between 2 harvest cycles is high.

Feature Description

To prevent duplicate Strings from being created, a cache is used.
The cache is keyed by the 3 components of the method information (class, name, signature). Each entry should expire after so many harvest cycles, to prevent memory leaking.

Additional context

Number of harvest cycles for cache expiration needs to be determined thru experimentation.
The same idea can be employed for the ThreadNameNormalizer, though the cache in this case can probably last longer.

Priority

Nice to Have