RFR: 8296734: JarVerifier:: mapSignersToCodeSource should cache in map [v3]

[pandaapo]

> The cache named `signerToCodeSource` in `JarVerifier` is never used now.

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

  Modify as reviews.

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/11072/files
  - new: https://git.openjdk.org/jdk/pull/11072/files/b3dbd279..ef4ba3df

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11072&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11072&range=01-02

  Stats: 45 lines in 4 files changed: 2 ins; 34 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/11072.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11072/head:pull/11072

PR: https://git.openjdk.org/jdk/pull/11072