COMPRESS-721 -- avoid reflection when possible in unpack200

[tballison]

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[tballison]

I added unit tests that fail when building without the ${argLine} --add-opens java.base/java.io=ALL-UNNAMED in the pom.xml

[garydgregory]

Hello @tballison

-1: These tests don't test anything new. They always pass, whether or not the changes to main are applied, inviting a regression to whatever you think you're fixing.

[tballison]

@garydgregory LOL...y, I added those when I was manually testing by removing the java >=17 profile in the pom.xml. However, as you point out, the build already fails spectacularly with existing tests when that is removed because of exactly this issue.

[tballison]

As a side note, the more aggressive fix is to get rid of reflection entirely. I chose to modify the existing code as little as possible on this PR, but happy to go bigger if desired.

[tballison]

Sorry for the noise, LegacyConstructorsTest obv still needs the java 17 profile. I confirmed we do not need new unit tests for pack200. The {{--add-opens}} which is necessary for existing unit tests masks the problems for unpack200.

[garydgregory]

Hello @tballison

There might be a way to do this without reflection, if so please provide it 😁 Otherwise, these untested changes are Just asking for a regression in the future...

[tballison]

fix incoming, again apologies for the noise.