RFR: 8306698: Add overloads to MethodTypeDesc::of [v2]

[Chen Liang]

> Please review this patch adding two new convenience methods that allows easier access to MethodTypeDesc instances and its associated CSR as well. This is a necessity to allow #13186 to reduce array copies in a few scenarios; the implementation of the two methods will be updated there.
> 
> Javadoc: https://cr.openjdk.org/~liach/8306698/1/java.base/java/lang/constant/MethodTypeDesc.html

Chen Liang has updated the pull request incrementally with one additional commit since the last revision:

  Update method type and specification, update tests

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Changes:
  - all: https://git.openjdk.org/jdk/pull/13599/files
  - new: https://git.openjdk.org/jdk/pull/13599/files/6463da2b..dc2a5a5d

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13599&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13599&range=00-01

  Stats: 55 lines in 2 files changed: 7 ins; 33 del; 15 mod
  Patch: https://git.openjdk.org/jdk/pull/13599.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13599/head:pull/13599

PR: https://git.openjdk.org/jdk/pull/13599