[ConstraintSystem] implement implicit pack materialization for abstract tuples instead of explicit '.element'

[sophiapoirier]

• Explanation: Solves the failure to type check the expansion of an abstract tuple shadowed by a global variable name by adding tracking of pack environments for pack elements to Constraint System and implementing implicit pack materialization for abstract tuples instead of explicit '.element'.
• Scope: Only impacts variadic generics.
• Issue: rdar://110401127
• Risk: Low.
• Testing: Added a new test case with code that previously emitted an error when type checking the expansion of an abstract tuple shadowed by a global variable name.
• Reviewer: @xedin @hborla
• Main branch PR: add tracking of pack environments for pack elements to Constraint System #67164 [ConstraintSystem] implement implicit pack materialization for abstract tuples instead of explicit '.element' #67292

[sophiapoirier]

@swift-ci please test