Update FreeType to 2.10.0 version from 2.9

Update FreeType to 2.10.0 version from 2.9

https://sourceforge.net/projects/freetype/files/freetype2/2.10.0/

This release brings one notable feature, namely support for color-layered outline glyphs (for example, scalable emoji glyphs). Additionally, the API reference has been completely overhauled and modernized, as already announced.

As usual, many minor fixes and corrections have been applied also;

CHANGES BETWEEN 2.9.1 and 2.10

I. IMPORTANT CHANGES

• A bunch of new functions has been added to access and process
  COLR/CPAL data of OpenType fonts with color-layered glyphs.

FT_Palette_Data_Get
Retrieve color palette data.
FT_Palette_Select
Select and activate a color palette for color-layered
glyphs.
FT_Palette_Set_Foreground_Color
Set text foreground color for palette index 0xFFFF.

FT_Get_Color_Glyph_Layer
Get color layers for a given glyph (using an interator
object).

FT_Bitmap_Blend
Blend one bitmap onto another with a given color.

• An experimental feature is the new behaviour of the
  `FT_LOAD_COLOR' load flag for color-layered glyphs: Internally
  it sets a flag so that if `FT_Render_Glyph' is called with
  `FT_RENDER_MODE_NORMAL' (or `FT_Load_Glyph' with
  `FT_LOAD_RENDER'), a default blending of the color glyph layers
  will happen automatically for convenience.

• As a GSoC 2018 project, Nikhil Ramakrishnan completely
  overhauled and modernized the API reference.

II. MISCELLANEOUS

• The logic for computing the global ascender, descender, and
  height of OpenType fonts has been slightly adjusted for
  consistency.

. If the `useTypoMetrics' flag (i.e., bit 7 in the `fsSelection'
field) in the `OS/2' table is set, use the `sTypo' fields in
`OS/2' unconditionally.
. Otherwise use the metrics data from the `hhea' table (if not
zero).
. Otherwise use the `sTypo' fields from the `OS/2' table (if not
zero).
. Otherwise use the `usWin' data from the `OS/2' table as a last
resort.

Variable fonts will apply the `MVAR' deltas to whichever metrics
were picked.

• `TT_Set_MM_Blend' could fail if call repeatedly with the same
  arguments.

• The precision of handling deltas in Variation Fonts has been
  increased. The problem did only show up with multidimensional
  designspaces.

• New function `FT_Library_SetLcdGeometry' to set up the geometry
  of LCD subpixels.

• FreeType now uses the `defaultChar' property of PCF fonts to set
  the glyph for the undefined character at glyph index 0 (as
  FreeType already does for all other supported font formats). As
  a consequence, the order of glyphs of a PCF font if accessed
  with FreeType can be different now compared to previous
  versions.

This change doesn't affect PCF font access with cmaps.

• `FT_Select_Charmap' has been changed to allow parameter value
  `FT_ENCODING_NONE', which is valid for BDF, PCF, and Windows FNT
  formats to access built-in cmaps that don't have a predefined
  `FT_Encoding' value.

• A previously reserved field in the `FT_GlyphSlotRec' structure
  now holds the glyph index.

• On Win32 platforms, the use of `_DLL' to build the library has
  been replaced with `DLL_EXPORT' and `DLL_IMPORT'.

• The usual round of fuzzer bug fixes to better reject malformed
  fonts.

• `FT_Outline_New_Internal' and `FT_Outline_Done_Internal' have
  been removed. These two functions were public by oversight only
  and were never documented.

• A new function `FT_Error_String' returns descriptions of error
  codes if configuration macro FT_CONFIG_OPTION_ERROR_STRINGS is
  defined.

• `FT_Set_MM_WeightVector' and `FT_Get_MM_WeightVector' are new
  functions limited to Adobe MultiMaster fonts to directly set and
  get the weight vector.

• Support for Position Independent Code as needed by systems that
  prohibit automatic address fixups, such as BREW, has been
  removed. [Compilation with modern compilers that use flags like
  `-fPIC' or `-fPIE' is not affected.]

• The `ftdump' demo program has new options `-c' and `-C' to
  display charmaps in compact and detailed format, respectively.
  Option `-V' has been removed.

• The `ftview', `ftstring', and `ftgrid' demo programs use a new
  command line option `-d' to specify the program window's width,
  height, and color depth.

• The `ftview' demo program now displays red boxes for zero-width
  glyphs.

• `ftglyph' has limited support to display fonts with
  color-layered glyphs. This will be improved later on.

• `ftgrid' can now display bitmap fonts also.

• The `ttdebug' demo program has a new option `-f' to select a
  member of a TrueType collection (TTC).

• Other various improvements to the demo programs.