RFR: 8362306: HotSpotJVMCIRuntime.getMirror can crash

[Doug Simon]

This PR fixes `HotSpotJVMCIRuntime.getMirror(ResolvedJavaMethod method)` and `HotSpotJVMCIRuntime.getMirror(ResolvedJavaField field)` so that they return null for `<clinit>` and an injected field respectively instead of crashing.

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Commit messages:
 - fixed bug in HotSpotJVMCIRuntime.getMirror for <clinit> and injected fields

Changes: https://git.openjdk.org/jdk/pull/26346/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26346&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8362306
  Stats: 68 lines in 5 files changed: 58 ins; 1 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/26346.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26346/head:pull/26346

PR: https://git.openjdk.org/jdk/pull/26346