RFR: 8288730: Lookup::accessClass(Class) should be generic on the type of `targetClass`

[liach]

Parameterizes `Lookup::accessClass` and `Lookup::ensureInitialized`. Updated an applicable use-site within JDK to benefit from this patch.

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Commit messages:
 - update use sites
 - 8288730: `Lookup::accessClass(Class)` should be generic on the type of `targetClass`

Changes: https://git.openjdk.org/jdk/pull/12984/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12984&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8288730
  Stats: 6 lines in 2 files changed: 2 ins; 1 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/12984.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12984/head:pull/12984

PR: https://git.openjdk.org/jdk/pull/12984