Cleanup J9_PROJECT_SPECIFIC code

[mgaudet]

Given that Eclipse OpenJ9 is now open, it makes it dramatically easier to move code from OMR to OpenJ9, allowing us to start cleaning up the J9_PROJECT_SPECIFIC guarded code.

This will of course be an epic, as there are currently over 700 instances of the #define. Perhaps the first thing to be discussed is a strategy, and priority.

• [ ] https://github.com/eclipse/omr/issues/6333
• [ ] https://github.com/eclipse/omr/issues/6334
• [ ] https://github.com/eclipse/omr/issues/6335
• [ ] https://github.com/eclipse/omr/issues/6336
• [ ] https://github.com/eclipse/omr/issues/6337
• [ ] https://github.com/eclipse/omr/issues/6338
• [ ] https://github.com/eclipse/omr/issues/6339
• [ ] https://github.com/eclipse/omr/issues/6340
• [ ] https://github.com/eclipse/omr/issues/4720 (TR::PPCDepImmSymInstruction)
• [ ] https://github.com/eclipse/omr/issues/6341
• [ ] https://github.com/eclipse/omr/issues/6342
• [ ] https://github.com/eclipse/omr/issues/1942
• [ ] https://github.com/eclipse/omr/issues/1883
• [x] https://github.com/eclipse/omr/issues/6343

[dsouzai]

Some bigger tasks as part of my initial cursory sweep through the code:

• Make TR_Debug Extensible
• Deal with TR_ResolvedMethod vs TR::ResolvedMethod
• Moving BCD queries to OpenJ9
• Make TR_FieldPrivatizer extensible to move things like TR_FieldPrivatizer::addStringInitialization and some other methods to OpenJ9
• Make TR_ProfiledNodeVersioning extensible
• Make TR_InvariantArgumentPreexistence extensible
• Make TR_LoopVersioner extensible for methods like TR_LoopVersioner::buildAwrtbariComparisonsTree
• VP
• VirtualGuardNOPInstructions