Add error for forward references in generic constraints (#7615)

* Add error for forward references in generic constraints

Change addresses issue #6545.

The slang compiler's type checker is unable to support cases where
a generic type parameter is referenced as a constraint before it is
declared. For example code like:

````
interface IFoo<T : IFloat>
{
}

void bar<Foo : IFoo<T>, T : IFloat>()
{
}
````

Is not supported, but will currently report a generic error like,

"(0): error 99999: Slang compilation aborted due to an exception
of class Slang::InternalError: unexpected: generic type constraint
during lowering"

This change adds a new check for this kind of code and reports an
error like,

"error 30117: generic constraint for parameter 'Foo' references type
parameter 'T' before it is declared"

when detected. Basic testing of this error is also added in a new
diagnostic test.

* Add error for forward refs in generic constiants update 1

* Add error for forward refs in generic constraints update 2

Revised algo in checkForwardReferencesInGenericConstraint to run
in O(n) instead of the previous O(n^2) using HashSets.

* Add error for forward refs in generic constraints update 3

-Update logic adding referenced decl's in collectReferencedDecls.
-Simplified error string logic.

* Add error for forward refs in generic constraints update 4

-Declare collectReferencedDecls in slang-check.h such that it can
 be used as a general utility function.

* format code

---------

Co-authored-by: slangbot <186143334+slangbot@users.noreply.github.com>

0 files changed, 0 insertions, 0 deletions