Support printing of snippets before binary encoding

[fjeremic]

As identified in [1] by @aviansie-ben there are numerous locations such as:

omr/compiler/z/codegen/ConstantDataSnippet.cpp

Line 651 in 0e780bb

trfprintf(pOutFile, "DC \t%p \t\t# ramMethod",*((intptr_t*)bufferPos));

omr/compiler/x/codegen/DataSnippet.cpp

Line 178 in 0e780bb

trfprintf(pOutFile, "%02x", bufferPos[i]);

omr/compiler/arm/codegen/ARMDebug.cpp

Line 839 in 0e780bb

else if (*((uintptr_t*)bufferPos) == 0xe28fe004) // This is a JNI method

where we dereference the pointer where the snippet is encoded in order to print the snippet to a trace log file. This is problematic if we wish to print the snippets before binary encoding. Such a need arises if we wish to print snippets during instruction selection for example, or in downstream projects which generate diagnostic trace files for crashes during compilation (for example if we crash during instruction selection, or during binary encoding of instructions).

We need to enhance the pretty-printing logic of snippets to support printing the snippet at any point in time, similarly to how we support this for instruction objects.

[1] #5053 (comment)