RFR: 8300140: ZipFile.isSignatureRelated returns true for files in META-INF subdirectories [v4]

[Eirik Bjorsnos]

> Some call sites of SignatureFileVerifier.isBlockOrSF fails to check that files reside in META-INF directly, and not in a subdirectory of META-INF.
> 
> The mentioned call sites needs updates to check and ignore such files.
> 
> A new test VerifyUnrelatedSignatureFiles is added which verifies that [*.SF, *.RSA] files in META-INF/ subdirectories are indeed ignored.

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

  To ensure that the "unrelated signature files" code path of JarVerifier is actually being exercised by our tests, add unrelated signature files also at the beginning of the test JAR

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Changes:
  - all: https://git.openjdk.org/jdk/pull/11976/files
  - new: https://git.openjdk.org/jdk/pull/11976/files/209d12ea..f264547a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11976&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11976&range=02-03

  Stats: 10 lines in 1 file changed: 6 ins; 1 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/11976.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11976/head:pull/11976

PR: https://git.openjdk.org/jdk/pull/11976