RFR: 8344824: CDS dump crashes when member_method of a lambda proxy is null

[Ioi Lam]

Since [JDK-8335583](https://bugs.openjdk.org/browse/JDK-8335583), we encode 64-bit pointers used by `RunTimeLambdaProxyClassKey` into 32-bit offsets. However, we didn't handle the cases where some of the pointers could be null.

In this PR, I have added an `or_null` variant of the functions that deal with pointer-to-offset encoding. The `or_null` variant allows an `nullptr` to be encoded with the 32-bit value of `0`.

I also renamed some of the functions to improve readability.

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Commit messages:
 - 8344824: CDS dump crashes when member_method of a lambda proxy is null

Changes: https://git.openjdk.org/jdk/pull/22313/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22313&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8344824
  Stats: 162 lines in 7 files changed: 143 ins; 4 del; 15 mod
  Patch: https://git.openjdk.org/jdk/pull/22313.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22313/head:pull/22313

PR: https://git.openjdk.org/jdk/pull/22313