RFR: 8286825: Linker naming cleanup

[Jorn Vernee]

This patch is a batch naming cleanup for the foreign linker implementation.

The naming changes are as follows:

  - ProgrammableInvoker -> DowncallLinker
  - ProgrammableUpcallHandler -> UpcallLinker
  - 'native invoker' -> 'downcall stub'
  - 'optimzed entry blob' -> 'upcall stub'
  - OptimizedEntryBlob -> UpcallStub
  - optimized_entry_frame -> upcall_stub_frame

Then renaming of some hotspot files:

  - universalNativeInvoker* -> downcallLinker*
  - universalUpcallHandler* -> upcallLinker*
  - foreign_globals* -> foreignGlobals* (to match existing convention)
  
Method, field, and other variable names are also adjusted accordingly.

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Commit messages:
 - 8275648: Linker naming bikeshed

Changes: https://git.openjdk.java.net/jdk/pull/8777/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8777&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8286825
  Stats: 2397 lines in 84 files changed: 1086 ins; 1090 del; 221 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8777.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8777/head:pull/8777

PR: https://git.openjdk.java.net/jdk/pull/8777