[acc] acc.loop verifier now requires parallelism determination flag (#143720)

The OpenACC specification for `acc loop` describe that a loop's
parallelism determination mode is either auto, independent, or seq. The
rules are as follows.
- As per OpenACC 3.3 standard section 2.9.6 independent clause: A loop
construct with no auto or seq clause is treated as if it has the
independent clause when it is an orphaned loop construct or its parent
compute construct is a parallel construct.
- As per OpenACC 3.3 standard section 2.9.7 auto clause: When the parent
compute construct is a kernels construct, a loop construct with no
independent or seq clause is treated as if it has the auto clause.
- Additionally, loops marked with gang, worker, or vector are not
guaranteed to be parallel. Specifically noted in 2.9.7 auto clause: If
not, or if it is unable to make a determination, it must treat the auto
clause as if it is a seq clause, and it must ignore any gang, worker, or
vector clauses on the loop construct.

The verifier for `acc.loop` was updated to enforce this marking because
the context in which a loop appears is not trivially determined once IR
transformations begin. For example, orphaned loops are implicitly
`independent`, but after inlining into an `acc.kernels` region they
would be implicitly considered `auto`. Thus now the verifier requires
that a frontend specifically generates acc dialect with this marking
since it knows the context.

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