RFR: 8333749: Consolidate ConstantDesc conversion in java.base

[Chen Liang]

In java.base, especially in bytecode generators, we have many different methods converting known valid Class and MethodType into ClassDesc and MethodTypeDesc. These conversions should be consolidated into the same utility method for the ease of future maintenance.

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Commit messages:
 - Missed license header
 - Consolidate class/mt to desc operations

Changes: https://git.openjdk.org/jdk/pull/19585/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19585&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8333749
  Stats: 160 lines in 8 files changed: 71 ins; 31 del; 58 mod
  Patch: https://git.openjdk.org/jdk/pull/19585.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19585/head:pull/19585

PR: https://git.openjdk.org/jdk/pull/19585