RFR: 8280120: [IR Framework] Add attribute to @IR to enable/disable IR matching based on the architecture [v2]

[Daniel Skantz]

> This PR adds support for platform features in IR Framework preconditions. This allows us to write platform-specific IR checks in the same .java test file.
> 
> Platforms considered in this PR are: operating system, arch, and data model (32 or 64-bit VM). Supported field values correspond to vm.simpleArch, os.family, and vm.bits, as used in jtreg `@requires` fields. We use the Platform library methods to accomplish this. Otherwise, the new preconditions work similar to the corresponding CPUFeature preconditions.
> 
> Testing: T1-T3, GHA.
> 
> Additional testing: Tweaked SW test succeeds with removed `@requires` field and added IR platform precondition, but fails with just removed `@requires` field on 32-bit Linux. Performed a few spot tests with incorrectly formatted preconditions, and with valid platform checks but invalid counts.

Daniel Skantz has updated the pull request incrementally with five additional commits since the last revision:

 - test method name
 - whitespace
 - whitespace
 - platformFeature to platform. Lint docs. Add more tests.
 - Add more platforms in IREncodingPrinter.java

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Changes:
  - all: https://git.openjdk.org/jdk/pull/15938/files
  - new: https://git.openjdk.org/jdk/pull/15938/files/e8d15462..2cfb95f9

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15938&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15938&range=00-01

  Stats: 262 lines in 7 files changed: 112 ins; 85 del; 65 mod
  Patch: https://git.openjdk.org/jdk/pull/15938.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15938/head:pull/15938

PR: https://git.openjdk.org/jdk/pull/15938