RFR: 8258471: "search codecache" clhsdb command does not work

[Yasumasa Suenaga]

`search codecache` command does not work as following:

hsdb> search codecache 0x7fedbd0aec90
java.lang.RuntimeException: Unable to deduce type of CodeBlob from address 0x00007fedbc85e810 (expected type nmethod, RuntimeStub, SafepointBlob, DeoptimizationBlob, or ExceptionBlob)
        at jdk.hotspot.agent/sun.jvm.hotspot.code.CodeCache.createCodeBlobWrapper(CodeCache.java:177)
        at jdk.hotspot.agent/sun.jvm.hotspot.memory.CodeHeap.iterate(CodeHeap.java:111)
        at jdk.hotspot.agent/sun.jvm.hotspot.code.CodeCache.iterate(CodeCache.java:185)
        at jdk.hotspot.agent/sun.jvm.hotspot.CommandProcessor$40.doit(CommandProcessor.java:1535)
        at jdk.hotspot.agent/sun.jvm.hotspot.CommandProcessor.executeCommand(CommandProcessor.java:2051)
        at jdk.hotspot.agent/sun.jvm.hotspot.CommandProcessor.executeCommand(CommandProcessor.java:2021)
        at jdk.hotspot.agent/sun.jvm.hotspot.CommandProcessor.run(CommandProcessor.java:1901)
        at jdk.hotspot.agent/sun.jvm.hotspot.CLHSDB.run(CLHSDB.java:99)
        at jdk.hotspot.agent/sun.jvm.hotspot.CLHSDB.main(CLHSDB.java:40)
        at jdk.hotspot.agent/sun.jvm.hotspot.SALauncher.runCLHSDB(SALauncher.java:280)
        at jdk.hotspot.agent/sun.jvm.hotspot.SALauncher.main(SALauncher.java:483)

I checked the Object which points 0x7fedbd0aec90, it was `VtableBlob`. It has been introduced in [JDK-8199406](https://bugs.openjdk.java.net/browse/JDK-8199406), but it did not change SA code.

SA should support `VtableBlob`.

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Commit messages:
 - 8258471: "search codecache" clhsdb command does not work

Changes: https://git.openjdk.java.net/jdk/pull/1800/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1800&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8258471
  Stats: 47 lines in 3 files changed: 46 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1800.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1800/head:pull/1800

PR: https://git.openjdk.java.net/jdk/pull/1800