RFR: 8265135: Reduce work initializing VarForms

[Claes Redestad]

This patch reduces work done initializing VarForms - mostly observed when loading each VarHandle implementation class.

- Lazily resolve MemberNames.
- Streamline MethodType creation. This reduces the number of MethodTypes created. 

Net effect is a reduction in bytecode executed per VH class by 50-60%.

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Commit messages:
 - Reduce work initializing VarForms

Changes: https://git.openjdk.java.net/jdk/pull/3472/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3472&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8265135
  Stats: 77 lines in 2 files changed: 37 ins; 30 del; 10 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3472.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3472/head:pull/3472

PR: https://git.openjdk.java.net/jdk/pull/3472