RFR: 8341775: Duplicate manifest files are removed by jarsigner after signing [v8]

[Kevin Driver]

> JDK-8341775: In the case where there is a *single* META-INF directory but potentially *multiple* manifest files of different cases, print a warning before selecting the first one and ignoring the rest (the current behavior should be maintained).

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

  review comments

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Changes:
  - all: https://git.openjdk.org/jdk/pull/22222/files
  - new: https://git.openjdk.org/jdk/pull/22222/files/4c78b9fd..64061d98

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=22222&range=07
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=22222&range=06-07

  Stats: 49 lines in 3 files changed: 40 ins; 5 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/22222.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22222/head:pull/22222

PR: https://git.openjdk.org/jdk/pull/22222