[flang] New implementation for checks for constraints C741 through C750

Summary:
Most of these checks were already implemented, and I just added references to
them to the code and tests. Also, much of this code was already
reviewed in the old flang/f18 GitHub repository, but I didn't get to
merge it before we switched repositories.

I implemented the check for C747 to not allow coarray components in derived
types that are of type C_PTR, C_FUNPTR, or type TEAM_TYPE.

I implemented the check for C748 that requires a data component whose type has
a coarray ultimate component to be a nonpointer, nonallocatable scalar and not
be a coarray.

I implemented the check for C750 that adds additional restrictions to the
bounds expressions of a derived type component that's an array.
These bounds expressions are sepcification expressions as defined in
10.1.11.  There was already code in lib/Evaluate/check-expression.cpp to
check semantics for specification expressions, but it did not check for
the extra requirements of C750.

C750 prohibits specification functions, the intrinsic functions
ALLOCATED, ASSOCIATED, EXTENDS_TYPE_OF, PRESENT, and SAME_TYPE_AS. It
also requires every specification inquiry reference to be a constant
expression, and requires that the value of the bound not depend on the
value of a variable.

To implement these additional checks, I added code to the intrinsic proc
table to get the intrinsic class of a procedure.  I also added an
enumeration to distinguish between specification expressions for
derived type component bounds versus for type parameters.  I then
changed the code to pass an enumeration value to
"CheckSpecificationExpr()" to indicate that the expression was a bounds
expression and used this value to determine whether to emit an error
message when violations of C750 are found.

I changed the implementation of IsPureProcedure() to handle statement
functions and changed some references in the code that tested for the
PURE attribute to call IsPureProcedure().

I also fixed some unrelated tests that got new errors when I implemented these
new checks.

Reviewers: tskeith, DavidTruby, sscalpone

Subscribers: jfb, llvm-commits

Tags: #llvm, #flang

Differential Revision: https://reviews.llvm.org/D79263