RFR: 8309673: Refactor ref_at methods in Serviceability ConstantPool [v2]

[Matias Saavedra Silva]

> The accessor methods in constantpool.cpp were previously cleaned up to allow for different types of indices to be used, distinguishing them by the bytecode. This patch adds the same changes to the hotspot serviceability agent code. Verified with tier 1-5 tests.

Matias Saavedra Silva has updated the pull request incrementally with one additional commit since the last revision:

  Removed unnecessary assignment

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Changes:
  - all: https://git.openjdk.org/jdk/pull/14385/files
  - new: https://git.openjdk.org/jdk/pull/14385/files/2ee60bd1..6630cb2c

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14385&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14385&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/14385.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14385/head:pull/14385

PR: https://git.openjdk.org/jdk/pull/14385