I tried to cross compile harfbuzz for Windows and an error was generated because `DWrite_1.h` was not found.
This happened because the filesystem is case sensitive and for this reason that include file was not found.
The right name of the file to be used is `dwrite_1.h`, with all letters not capitalized:
https://docs.microsoft.com/en-us/windows/desktop/api/dwrite_1/
I also verified in the installation of VS2017 with Windows Kit v10 and in that place it was also lower case.
So, in my opinion it should be better to change this.

Also checks if DWriteCreateFactory() has been executed successfully.

Fixes https://github.com/harfbuzz/harfbuzz/pull/1783

This makes it possible to include all .cc files into build, even if not
building CoreText, Uniscribe, etc.

This was mostly to help custom builders.  But also means that we can
include all files in our own build system.  Not sure if we should.
Definitely simplifies things, but slightly only.

Can be useful when using HarfBuzz for font loading and shaping
but using DirectWrite for rendering.

https://github.com/harfbuzz/harfbuzz/issues/1641

It makes a hb_face_t from IDWriteFontFace, useful when using
DirectWrite facilities for font selection, loading and rendering
but using harfbuzz for shaping.

Fixes #1548 hopefully

hb-directwrite.cc: In constructor 'TextAnalysis::TextAnalysis(const wchar_t*, uint32_t, const wchar_t*, DWRITE_READING_DIRECTION)':
hb-directwrite.cc:489:18: error: 'TextAnalysis::mText' will be initialized after [-Werror=reorder]
   const wchar_t* mText;
                  ^~~~~
hb-directwrite.cc:488:12: error:   'uint32_t TextAnalysis::mTextLength' [-Werror=reorder]
   uint32_t mTextLength;
            ^~~~~~~~~~~
hb-directwrite.cc:282:3: error:   when initialized here [-Werror=reorder]
   TextAnalysis (const wchar_t* text, uint32_t textLength,
   ^~~~~~~~~~~~
hb-directwrite.cc: In function 'hb_bool_t _hb_directwrite_shape_full(hb_shape_plan_t*, hb_font_t*, hb_buffer_t*, const hb_feature_t*, unsigned int, float)':

No other shaper will need shape_plan_data, by definition.  So, remove
abstraction layer and always create hb_ot_shape_plan_t as part of
hb_shape_plan_t.

Sorry for the noise, downstream custom builders.  Please adjust.

Fixes #791.

Fixes https://github.com/behdad/harfbuzz/issues/615

We'll see which bots I broke.

Part of fixing https://github.com/behdad/harfbuzz/pull/605