Amalgam builds are broken when both DirectWrite and Uniscribe are enabled

[khaledhosny]

Both files define structs with similar names since #3034. Need to move that code to a shared place and templatize it after all.

[behdad]

You can rename them to be unique for now.

I would do it but I can't build the directwrite code.

[15mins later]

I checked the code. I believe the DWrite structs were designed to be byte-compatible with the uniscribe ones. So I believe we can use non-templatized shared code. Just need to define two structs and have static asserts that their sizes match the uniscribe / dwrite one, and use those.

• Unify OPENTYPE_FEATURE_RECORD and DWRITE_FONT_FEATURE into hb_ms_feature_t.
• Unify TEXTRANGE_PROPERTIES and DWRITE_TYPOGRAPHIC_FEATURES into hb_ms_features_t.