Research whether remaining `IgnoreImpCasts` calls should be changed to `IgnoreParenImpCasts`

[mattmccutchen-cci]

Several places in the 3C code use IgnoreImpCasts instead of IgnoreParenImpCasts, and at least one of those resulted in a bug (#543). This issue is to research whether the other calls should be changed too.

There's at least one more case where it looks like parentheses around a function name might crash 3C. I expected the following code might trigger the crash:

int *p = (malloc)(sizeof(int));

except the 3C conversion is blocked from running at all by a compiler error ("expected a type argument list for a bounds-safe interface call in a checked scope") that I think may reflect a Checked C compiler bug for two reasons (the code is not in a checked scope, and I would expect 3C's use of -f3c-tool mode to suppress errors of this nature).

[mattmccutchen-cci]

It turns out that the crash case I described above can in fact be triggered due to an underlying problem that currently exists with PersistentSourceLoc collisions in the TypeParamBindings map; we saw an example of this in the version of PtrDist ks in analyse-conv. #569 will fix the crash in this case; #568 remains open for the underlying problem. This issue remains open for the remaining IgnoreImpCasts calls.