RFR: 8297036: Generalize C2 stub mechanism [v2]

[Roman Kennke]

> Currently, we have two implementations of out-of-line stubs in C2, one for safepoint poll stubs (C2SafepointPollStubTable in output.hpp) and another for nmmethod entry barriers (C2EntryBarrierStubTable in output.hpp). I will need a few more for Lilliput: One for checking lock-stack size in method prologue, one for handling lock failures (both for fast-locking), and another one for load-klass slow-path. It would be good to generalize the mechanism and consolidate the existing uses on the new general mechanism.
> 
> Testing:
>  - [x] tier1 (x86_64, x86_32, aarch64)
>  - [x] tier2 (x86_64, x86_32, aarch64)
>  - [x] tier3 (x86_64, x86_32, aarch64)

Roman Kennke has updated the pull request incrementally with one additional commit since the last revision:

  Don't measure code size in advance, but verify it after emitting

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Changes:
  - all: https://git.openjdk.org/jdk/pull/11188/files
  - new: https://git.openjdk.org/jdk/pull/11188/files/30a22232..ed2ab014

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11188&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11188&range=00-01

  Stats: 75 lines in 4 files changed: 17 ins; 52 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/11188.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11188/head:pull/11188

PR: https://git.openjdk.org/jdk/pull/11188