Represent each parameterized test function argument as a separate element in Test.Case.arguments

[stmontgomery]

Represent each parameterized test function argument as a separate element in Test.Case.arguments, including tuple types which have been de-structured into discrete function parameters.

Motivation:

This is an enhancement meant to represent arguments of parameterized test functions in Test.Case instances in a more useful way, and facilitate progress towards allowing (re-)running specific argument(s) of such functions.

Modifications:

• Introduce a struct Test.Case.Argument which represents one argument passed to one parameter of a parameterized test function. This includes each argument's associated Test.ParameterInfo.
• Change the Test.Case.arguments property to be an array of the new struct type.
• Enhance Test.Case.Generator to generate Test.Case instances using the new argument structure—including de-structuring tuples into their constituent elements when needed. It accomplishes this more efficiently now using some specialized generic overloads.
• Remove Test.Case.arguments(pairedWith:) function, since it's no longer necessary given the arguments property already pairs these values.
• Introduce a convenience utility for testing purposes only, which handles errors thrown in eventHandler closures.

Checklist:

• Code and documentation should follow the style of the Style Guide.
• If public symbols are renamed or modified, DocC references should be updated.

[stmontgomery]

@swift-ci please test

[stmontgomery]

@swift-ci please test

[stmontgomery]

@swift-ci please test

[stmontgomery]

@swift-ci please test