doc: Add missing sections and symbols for public docs

This adds a number of items to the documentation for which code docs
exist, and also adds sections for cairo-skia and cairo-surface-observer.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=48784

Signed-off-by: Bryce Harrington <b.harrington@samsung.com>
doc: Drop a couple quartz routines which distcheck claims don't exist

These routines actually do exist in the source code, and have proper
documentation, so I'm not sure why distcheck dislikes them, but it's
happier without these listed.

Signed-off-by: Bryce Harrington <b.harrington@samsung.com>
Mark recently added _cairo_output_stream_print_matrix private symbol

This fixes a distcheck error about a local PLT entry.

Signed-off-by: Bryce Harrington <b.harrington@samsung.com>
surface: Make parameter naming consistent between header and impl

This fixes this set of distcheck errors generating docs:

  src/cairo-surface.c:1668: warning: Parameter described in source code
  comment block but does not exist. FUNCTION:
  cairo_surface_set_device_scale Parameter: sx.

  src/cairo-surface.c:1668: warning: Parameter described in source code
  comment block but does not exist. FUNCTION:
  cairo_surface_set_device_scale Parameter: sy.

  src/cairo-surface.c:1668: warning: Parameter description for
  cairo_surface_set_device_scale::x_scale is missing in source code
  comment block.

  src/cairo-surface.c:1668: warning: Parameter description for
  cairo_surface_set_device_scale::y_scale is missing in source code
  comment block.

Signed-off-by: Bryce Harrington <b.harrington@samsung.com>
Document that libglib2.0-doc is needed to avoid some xref warnings

Signed-off-by: Bryce Harrington <b.harrington@samsung.com>
skia: Add section definitions and code docs for skia backend

This fixes several distcheck errors regarding missing code docs.

The skia backend was added in commit d7faec02, which was included in the
1.10 release.

Signed-off-by: Bryce Harrington <b.harrington@samsung.com>
Fix warnings from check-doc-syntax.sh

$ ./check-doc-syntax.sh
Checking documentation for incorrect syntax
./cairo-types-private.h (148): WARNING: cairo_hash_entry_t: missing 'Since' field (is it a private type?)
./cairo-types-private.h (161): WARNING: cairo_hash_entry_t: not found
./cairo-types-private.h (175): WARNING: cairo_lcd_filter_t: missing 'Since' field (is it a private type?)
./cairo-cache-private.h (85): WARNING: cairo_cache_entry_t: missing 'Since' field (is it a private type?)
./cairo-region.c (857): WARNING: cairo_region_overlap_t: not found
./cairo-raster-source-pattern.c (62): WARNING: SECTION:cairo-raster-source 'Since' field in non-public element

The warnings about missing 'Since' fields are fixed by changing the
documentation comment so that the script can see that these are private types.

The documentation for cairo_region_overlap_t gets moved to cairo.h, just like
e.g. the documentation for cairo_status_t.

The 'Since' field from the SECTION:cairo-raster-source is removed, because this
kind of field is needed on the individual functions and structs, not on the
section.

Thanks to Bryce Harrington for bringing this up!

Signed-off-by: Uli Schlachter <psychon@znc.in>
Tested-by: Bryce Harrington <b.harrington@samsung.com>