RFR: 8362306: HotSpotJVMCIRuntime.getMirror can crash [v6]

[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.

Doug Simon has updated the pull request incrementally with one additional commit since the last revision:

  replaced use of JVMCIENV with JVMCI_CHECK_NULL in getDeclaredFieldsInfo

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Changes:
  - all: https://git.openjdk.org/jdk/pull/26346/files
  - new: https://git.openjdk.org/jdk/pull/26346/files/fd44d95c..d62c74d9

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26346&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26346&range=04-05

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 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