[FIXED JENKINS-42753] No more closure translation!

[abayer]

• JENKINS issue(s):
  • JENKINS-42753
• Description:
  • This enables/fixes a lot of things, here specifically allowing parameters to be referenced in agent { label ... }, though it sadly does not allow use of something from environment at the top level in an agent at the top level (or same for environment/agent at the same stage level) due to JENKINS-41890 taking priority - i.e., we evaluate environment after we evaluate agent. May revisit that later. ANYWAY.

• Implementation works, all existing tests pass.
• Ok, technically, all but one - BasicModelTest#libraryObjectInScript is blowing up over import issues. Needs more investigation, may block this whole thing, we'll see!
• Find more complicated usage patterns, such as those at JENKINS-42777, and make sure those still work too.
• No, seriously, TEST THE CRAP OUT OF THIS. I'm willing to bet there at least a couple regressions I haven't found due to not having coverage of those particular syntactic quirks, and I am not releasing this until we're 99% confident we've caught every possible regression.

• Documentation changes:
  • n/a - this is a purely internal change. Any changes in user-facing behavior would be regressions we need to find before we release anyway.
• Users/aliases to notify:
  • @reviewbybees
  • @rsandell

[abayer]

Incorporated JENKINS-42829 as well - notes from that commit:

Now that we're script.evaluate(...)ing everything, we need to be sure
that anything defined elsewhere in the Jenkinsfile outside the
pipeline block is available in that evaluated scope. This...is the
most effective way I can come up with to do so. It has some risks -
something with side effects could be problematic, but that's not a use
case we're keen on supporting anyway.

[abayer]

This is a dead attempt, closing.

[jglick]

Superseded by #174 perhaps?