RFR: 8300259: Add test coverage for processing of pending block files in signed JARs [v2]

[Eirik Bjorsnos]

> This PR adds test coverage for pending block files in signed JAR files
> 
> A signed JAR has pending block files if the block file [RSA, DSA, EC] comes before the corresponding signature file [SF] in the JAR. 
> 
> JarVerifier.processEntry supports processing of such pending block files, but this code path does not seem to be exercised by current test.
> 
> The new test PendingBlocksJar checks that signed JARs  with pending blocks are processed correctly, both for the valid and invalid cases.

Eirik Bjorsnos has updated the pull request incrementally with two additional commits since the last revision:

 - Make it more clear in the @summary tag that it is the block file that is pending, not the signature file
 - Renamed test from PendingBlocksJar to more descriptive SignedJarPendingBlock

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/12009/files
  - new: https://git.openjdk.org/jdk/pull/12009/files/acaad55c..162744ff

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12009&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12009&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/12009.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12009/head:pull/12009

PR: https://git.openjdk.org/jdk/pull/12009