[6.0][PubGrub] Narrow down cases when pre-release decisions are marked inv…

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…alid

• Explanation:

  Pre-release decisions are valid if the derived range they were inferred from supports pre-release versions.

  Currently, after deriving a pre-release assignment, the solver would assert
  in some circumstances depending on order in which the dependencies are specified in the manifest.

  This change makes it possible to infer pre-release verison of a package even when intermediate derivations did not support pre-release versions.

  For example one package could declare swift-syntax dependency as 508.0.1 ..< 601.0.0 and another could narrow it to 600.0.0-latest ..< 601.0.0.

  Since the most constrained range in such case supports pre-releases a decision
  to use the lastest pre-release version of 600.0.0 should be valid if there
  is no 600.0.0 release yet.

  It's important to note that on each path a decision for a package is always
  made based on the last undecided term's requirements which means - based on the current semantics - if such derivation doesn't support pre-release,
  even though intermediate ones did, the solver would select a released version.
  This PR is not aim to change that.

  There is a caveat which we cannot narrowly fix - if package depends on an exact
  pre-release version the inference is going to fail when there is another dependency
  to the same package that doesn't support pre-releases. For example:

  Package A depends on packages B and C as follows:

  A depends on B = 0.0.1-alpha and C = 1.0.0 B version 0.0.1-alpha has no dependencies
  C version 1.0.0 depends on B - 0.0.1 ..< 0.0.2

  In this situation the solver would fail because 0.0.1-alpha does not satisfy range - 0.0.1 ..< 0.0.2 inferred from C.

  • Delays version decisions for packages with pre-release ranges until there are no more packages without pre-release versions. This also means that if a previous decision narrows down the range to releases-only the package would be made a contender on the next step of the solver.

  • Relaxes the isValidDecision check for pre-release decisions but makes sure that the last derivation supports pre-release versions.

  In situations like
  InternalError on packages with -latest component in their version #7658 and InternalError: Expected root cause #7643 the solver would no longer assert and would produce a solution with a pre-release version for swift-syntax.

• Main Branch PR: [PubGrub] Narrow down cases when pre-release decisions are marked invalid #7799

• Risk: Low (These changes only affect packages that have pre-release version dependencies in a very narrow circumstances where there is another dependency that isn't a pre-release).

• Reviewed By: @MaxDesiatov

• Resolves: rdar://130112167 InternalError on packages with -latest component in their version #7658 InternalError: Expected root cause #7643

• Testing: Existing test-cases were modified and new tests were added.

(cherry picked from commit 43fd240)

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@swift-ci please test