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)
------------- Commit messages: - 8287064: Modernize ProxyGenerator.PrimitiveTypeInfo Changes: https://git.openjdk.java.net/jdk/pull/8801/files Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8801&range=00 Issue: https://bugs.openjdk.java.net/browse/JDK-8287064 Stats: 79 lines in 1 file changed: 14 ins; 41 del; 24 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
