This reverts commit 8f638591.

Based on the FontCacheFuchsia used in the Blink renderer

libtxt: extend Minikin to find a fallback font if its font collection can not match a given character (#4623)

Minikin layout uses a FontCollection containing a list of pre-selected fonts
for a particular font family.  This patch extends the FontCollection to invoke
a hook provided by libtxt if layout sees a character that can not be rendered
by any font in the collection.

* Change the Minikin lock to a recursive mutex.  This is required because the
  fallback font provider may create new fonts during a layout operation that
  already holds the lock.
* Implement a fallback font provider hook that queries Skia for fonts matching
  an unrecognized character.
* Maintain a cache of fallback fonts.  Prepopulate the cache with fonts
  covering some commonly used character classes.
* Add a last resort font list for cases where Skia's font manager can not
  find any font for a character (similar to Blink's FontCache::getLastResortFallbackFont)

We need to handle the error case properly.

This adds support for semantics traversal ordering.

It is a companion to flutter/flutter#14060, adding support for a sortIndex in the semantics data passed to the engine.

Addresses flutter/flutter#12187

* GetGlyphPositionAtCoordinate maps points within the right half of a
  glyph to the next position
* The second pass in RepeatLayoutParagraph was at the borderline between 5
  and 6 lines in the Minikin line breaker.  Add text to ensure that the text
  fills 12 lines at half width and 6 lines at full width.

This simplifies iteration over graphemes and fixes an off-by-one error seen
when handling RTL runs.

This change will make it easier to transition to FIDL2.

Use @Available checks for iOS 11 features

Instead, use the underlying libasync wait primitives.

Only implement `application:performActionForShortcutItem:completionHandler:` on iOS 9.0+. And fix some tests. (#4600)

This reverts commit 47cae4d8.
This reverts commit 9b9de0e5.

... which caused trouble for a11y "select all".

Revert "libtxt: extend Minikin to find a fallback font if its font collection can not match a given character (#4595)" (#4609)

This reverts commit 9a402241.

We now run clang-format checks before running licenses and other tests.
Since clang-format runs quickly, this allows these diffs to be caught
first, without much real delay to other checks.

Each time we update the clang toolchain, we've needed to deal with diffs
resulting from new clang-format defaults and improvements to existing
settings. This reduces diff checking to just the diffed lines.

vulcan_provider.{cc.h} were added in
fb9782a5. This updates the licenses
golden file to include them and fix the current breakage on Travis.

libtxt: extend Minikin to find a fallback font if its font collection can not match a given character (#4595)

Minikin layout uses a FontCollection containing a list of pre-selected fonts
for a particular font family.  This patch extends the FontCollection to invoke
a hook provided by libtxt if layout sees a character that can not be rendered
by any font in the collection.

* Change the Minikin lock to a recursive mutex.  This is required because the
  fallback font provider may create new fonts during a layout operation that
  already holds the lock.
* Implement a fallback font provider hook that queries Skia for fonts matching
  an unrecognized character.
* Maintain a cache of fallback fonts.  Prepopulate the cache with fonts
  covering some commonly used character classes.
* Add a last resort font list for cases where Skia's font manager can not
  find any font for a character (similar to Blink's FontCache::getLastResortFallbackFont)

Required by the spec; see '6.7.4. Queue Family Ownership Transfer'
of Vulkan 1.0.66.

Transitioning the image layout also fixes an image resolve failure
issue introduced by optimizations present in the intel mesa vulkan
driver v17.2.

For more consistent access to base vulkan functionality owned
elsewhere.

This reverts commit 89b6d435.

Apparently the clang toolchain is still hitting issues. Will give this
another go after the next clang toolchain update.

Guard code that deals with iOS safe area insets behind an @Available
check.

This cleans up some old TODOs from before out clang toolchain supported
@Available.

Consolidates the asset path lookup logic from FlutterDartProject and FlutterMain().

* Lookup FTLAssetsPath when deducing assets path on ios

* WS

* Proper fix

* Another whitespace fix

* Allow embedder clients to provide a resource context. Closes flutter/flutter#14263.

See https://github.com/flutter/flutter/pull/14275 for framework side change.

Also includes some minor clean-ups for consistency. 

Required for https://github.com/flutter/flutter/issues/13469.