[jdk11u-dev] RFR: 8292713: Unsafe.allocateInstance should be intrinsified without UseUnalignedAccesses

[Fei Yang]

Backport to improve arm32 performance in 11u and riscv-port in: https://github.com/openjdk/riscv-port-jdk11u/pull/3.
This is not a clean backport as the function has been moved to new file and renamed. 

I checked the 11u related code and I think the following analysis on the JBS description is still true for 11u:
"The intrinsic is currently only implemented in C2. I see no reason for this intrinsic to depend on `UseUnalignedAccesses`: what `LibraryCallKit::inline_unsafe_allocate()` does seems similar to what the regular `Parse::do_new()` does, namely doing the clinit barrier and then delegating into `GraphKit::new_instance`."

Tested with the initial riscv-port in: https://github.com/openjdk/riscv-port-jdk11u/pull/3

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Commit messages:
 - 8292713: Unsafe.allocateInstance should be intrinsified without UseUnalignedAccesses

Changes: https://git.openjdk.org/jdk11u-dev/pull/2125/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=2125&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8292713
  Stats: 2 lines in 1 file changed: 1 ins; 1 del; 0 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/2125.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev.git pull/2125/head:pull/2125

PR: https://git.openjdk.org/jdk11u-dev/pull/2125