Fix parsing of for-loops

[CyrusNajmabadi]

Fixes #76439

Introduced with #75632. So only in 17.13p2. So fixing this will prevent the regression from making it out.

The core issue here was an incorrect understanding i had with order-of-evaluation and storage of values for args when invoking methods. Specifically, i thought that the following:

M(
   x = y(),
   Z(ref x));

Was evaluated effectively as:

xloc = y();
__z_val = Z(ref xloc);
M(xloc, __z_val);

But it is not. rather, it is:

__x_val = x = y();
__z_val = M(ref x);
M(__x_val, __z_val);

In other words, i thought the call to M woudl see the value of 'x' after the call to Z, while it actually evaluates and stores that value prior to the call to Z.

This mattered during parsing as we use that value to store skipped tokens onto. So if we use the value prior to updating, we lose those skipped tokens, leading to an invalid incremental parse.

[CyrusNajmabadi]

@dotnet/roslyn-compiler @RikkiGibson ptal

[RikkiGibson]

It looks like this comment was specific to secondSemicolonToken before, is it still relevant now?

[CyrusNajmabadi]

yes/ will move.

[CyrusNajmabadi]

@RikkiGibson this is ready for another pass.