RFR: 8310494: Do not include constantPool.hpp from instanceKlass.hpp

[Ioi Lam]

instanceKlass.hpp is needed quite frequently for HotSpot C++ sources, but constantPool.hpp is much less frequently.

This PR is the first step of reducing the inclusion of constantPool.hpp, by removing it from instanceKlass.hpp

I moved a bunch of inline functions into instanceKlass.cpp. These don't seem to be performance related.

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Commit messages:
 - 8310494: Do not include constantPool.hpp from instanceKlass.hpp

Changes: https://git.openjdk.org/jdk/pull/14597/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14597&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8310494
  Stats: 59 lines in 5 files changed: 36 ins; 11 del; 12 mod
  Patch: https://git.openjdk.org/jdk/pull/14597.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14597/head:pull/14597

PR: https://git.openjdk.org/jdk/pull/14597