[flang] Fix parsing and semantics for array element substring%KIND/%LEN

A type-param-inquiry of %KIND or %LEN applies to a designator, and
so must also be allowed for a substring.  F18 presently (mis)parses
instances of a type-param-inquiry as structure component references
and then fixes them in expression semantics when types are known and
we can distinguish them.  But when the base of a type-param-inquiry is
a substring of an array element, as in "charArray(i)(j:k)%len",
parsing fails.

Adjust the grammar to parse these cases, and extend expression semantics
to process the new production.

Differential Revision: https://reviews.llvm.org/D130375