RFR: 8287064: Modernize ProxyGenerator.PrimitiveTypeInfo [v2]

[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 incrementally with one additional commit since the last revision:

  Convert PrimitiveTypeInfo to an enum

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/8801/files
  - new: https://git.openjdk.java.net/jdk/pull/8801/files/16f3de8f..be9987bb

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=8801&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=8801&range=00-01

  Stats: 10 lines in 1 file changed: 0 ins; 0 del; 10 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