[foreign-memaccess+abi] RFR: 8310659: The jar tool should support allowing access to restricted methods from executable jars [v4]

[Jorn Vernee]

> Add `Enable-Native-Access` jar attribute. `Enable-Native-Access: true` is equal to passing `--enable-native-access=ALL-UNNAMED` on the command line when running an executable jar (using `-jar <jar file>`).
> 
> Question: right now I've implemented this to check if the attribute value is exactly `true`, otherwise it is ignored. Should we only allow `true` or `false`, and throw an error on other values?
> 
> Reviewer note: I've factored some of a test code for analyzing output to `TestEnableNativeAccessBase` for the enable native access tests.

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

  error when flag is set to false

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Changes:
  - all: https://git.openjdk.org/panama-foreign/pull/843/files
  - new: https://git.openjdk.org/panama-foreign/pull/843/files/86dc7be7..7e467593

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=panama-foreign&pr=843&range=03
 - incr: https://webrevs.openjdk.org/?repo=panama-foreign&pr=843&range=02-03

  Stats: 117 lines in 9 files changed: 56 ins; 34 del; 27 mod
  Patch: https://git.openjdk.org/panama-foreign/pull/843.diff
  Fetch: git fetch https://git.openjdk.org/panama-foreign.git pull/843/head:pull/843

PR: https://git.openjdk.org/panama-foreign/pull/843