RFR: 8303684: Lift upcall sharing mechanism to AbstractLinker (mainline)

[Jorn Vernee]

Port of: https://github.com/openjdk/panama-foreign/pull/791 which lifts the sharing mechanism for upcall stubs to AbstractLinker. 

This also speeds up upcall stub linking:

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Commit messages:
 - update benchmark
 - update copyright years
 - 8302346: Lift upcall sharing mechanism to AbstractLinker

Changes: https://git.openjdk.org/jdk/pull/12883/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12883&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8303684
  Stats: 155 lines in 16 files changed: 54 ins; 34 del; 67 mod
  Patch: https://git.openjdk.org/jdk/pull/12883.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12883/head:pull/12883

PR: https://git.openjdk.org/jdk/pull/12883