RFR: 8304031: Classfile API cannot encode Primitive Class as Condy [v3]

[Chen Liang]

> Without this patch, the Classfile API tries to encode PrimitiveClassDesc as CONSTANT_Class_info and error in `toInternalName`.

Chen Liang has updated the pull request incrementally with one additional commit since the last revision:

  PrimitiveClassConstantTest check the other 2 API endpoints, move to junit

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Changes:
  - all: https://git.openjdk.org/jdk/pull/12996/files
  - new: https://git.openjdk.org/jdk/pull/12996/files/df3ed0c0..74021d23

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12996&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12996&range=01-02

  Stats: 18 lines in 1 file changed: 10 ins; 2 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/12996.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/12996/head:pull/12996

PR: https://git.openjdk.org/jdk/pull/12996