RFR: 8262028: Make InstanceKlass::implementor return InstanceKlass

[Harold Seigel]

Please review this small fix to change the parameter and return types from Klass* to InstanceKlass* in the InstanceKlass::*implementor() functions.

The fix was tested with Mach5 tiers 1 and 2 on Linux, Mac OS, and Windows, and tiers 3-5 on Linux x64.

Thanks, Harold

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Commit messages:
 - 8262028: Make InstanceKlass::implementor return InstanceKlass

Changes: https://git.openjdk.java.net/jdk/pull/2755/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2755&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8262028
  Stats: 36 lines in 4 files changed: 0 ins; 0 del; 36 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2755.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2755/head:pull/2755

PR: https://git.openjdk.java.net/jdk/pull/2755