Getting rid of more (FX_LPCWSTR) casts and fixing two bugs revealed by this.

Since casts to FX_LPCWSTR have been shown to hide bugs I tried removing
more of them, targeting those places where a cast was used to force a
conversion from CFX_WideString to FX_LPCWSTR, replacing these casts with
calls to the newly added .c_str() function. This revealed two places
where the cast was hiding a bug -- where ->c_str() was required instead!

This removes ~33 FX_LPCWSTR casts and there are ~31 left, many of which
will go away in some future change.

Also includes this change:

Removing unnecessary casts from wchar_t* to wchar_t*, by various names.

Original patch from Bruce Dawson(brucedawson@chromium.org)

R=bo_xu@foxitsoftware.com, tsepez@chromium.org

Review URL: https://codereview.chromium.org/733693003
Replace manual/error-prone/hard-to-verify arraysize calculations with safe FX_ArraySize macro.

pdfium has numerous places where the number of elements in an array is
calculated with expressions like:

    sizeof(cFormats)/sizeof(FX_LPCWSTR)

This is suboptimal because it is verbose, it is easy to get wrong, and
it cannot be determined through casual inspection whether the code is
correct. It will give incorrect results if cFormats is a pointer instead
of an array and it will give incorrect results if FX_LPCWSTR is not the
type of the array elements.

The FX_WSTRC macro in fx_string.h which I fixed was particularly scary
because it would silently misbehave if passed a pointer.

The FX_ArraySize macro which I have added and started using (taken from
arraysize in v8's macros.h) is easier to use and will always give correct
results. If passed a pointer it will fail to compile.

For this change I only fixed instances of sizeof(FX_LPCWSTR). There
appear to be about 150 other places in the pdfium code that could
benefit from using FX_ArraySize.

R=bo_xu@foxitsoftware.com, tsepez@chromium.org

Review URL: https://codereview.chromium.org/729293003
Merge remote-tracking branch 'origin/master' into light_version