RFR: 8287064: Modernize ProxyGenerator.PrimitiveTypeInfo [v3]

[liach]

> Simplify opcode handling, use `final` in `PrimitiveTypeInfo`, and replace the hash map with a simple lookup, similar to what's done in [JDK-8284880](https://bugs.openjdk.java.net/browse/JDK-8284880) (#8242)

liach has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:

 - Merge branch 'master' into proxy-primitivetypeinfo
 - Convert PrimitiveTypeInfo to an enum
 - 8287064: Modernize ProxyGenerator.PrimitiveTypeInfo

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/8801/files
  - new: https://git.openjdk.java.net/jdk/pull/8801/files/be9987bb..96c0835e

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=8801&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=8801&range=01-02

  Stats: 37306 lines in 626 files changed: 8637 ins; 27109 del; 1560 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8801.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8801/head:pull/8801

PR: https://git.openjdk.java.net/jdk/pull/8801