RFR: 8267338: [JVMCI] revive JVMCI API removed by JDK-8243287

[Doug Simon]

This PR revives ResolvedJavaType.getHostClass to preserve JVMCI compatibility. The revived method just returns `null`.

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Commit messages:
 - revive ResolvedJavaType.getHostClass

Changes: https://git.openjdk.java.net/jdk/pull/4099/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4099&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8267338
  Stats: 8 lines in 1 file changed: 8 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4099.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4099/head:pull/4099

PR: https://git.openjdk.java.net/jdk/pull/4099