RFR: 8287064: Modernize ProxyGenerator.PrimitiveTypeInfo [v4]

[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:

  Make primitive type info more reader friendly

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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/96c0835e..6d171268

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=8801&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=8801&range=02-03

  Stats: 26 lines in 1 file changed: 7 ins; 1 del; 18 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