Adds the hasStrings method for Mac, and improves the state of unit testing on Mac.

Fixes the following compilation errors:
../../flutter/shell/platform/linux/fl_platform_plugin.cc:89:7: error: use of undeclared identifier 'strcmp'
  if (strcmp(format, kTextPlainFormat) != 0) {
      ^
../../flutter/shell/platform/linux/fl_platform_plugin.cc:127:7: error: use of undeclared identifier 'strcmp'
  if (strcmp(method, kSetClipboardDataMethod) == 0)
      ^
../../flutter/shell/platform/linux/fl_platform_plugin.cc:129:12: error: use of undeclared identifier 'strcmp'
  else if (strcmp(method, kGetClipboardDataMethod) == 0)
           ^
../../flutter/shell/platform/linux/fl_platform_plugin.cc:131:12: error: use of undeclared identifier 'strcmp'
  else if (strcmp(method, kSystemNavigatorPopMethod) == 0)
           ^
../../flutter/shell/platform/linux/fl_view.cc:194:7: error: use of undeclared identifier 'strcmp'
  if (strcmp(pspec->name, "scale-factor") == 0) {
      ^
../../flutter/shell/platform/linux/fl_engine.cc:67:18: error: use of undeclared identifier 'strrchr'
  gchar* match = strrchr(l, '@');
                 ^
../../flutter/shell/platform/linux/fl_engine.cc:75:11: error: use of undeclared identifier 'strrchr'
  match = strrchr(l, '.');
          ^
../../flutter/shell/platform/linux/fl_engine.cc:83:11: error: use of undeclared identifier 'strrchr'
  match = strrchr(l, '_');
          ^
Signed-off-by: NDamian Wrobel <dwrobel@ertelnet.rybnik.pl>

There was a problem with GoB that made all the builders fail on old
commits. As the last commit was successful we need to force a new
execution to unblock the tree.

Migrate to autoninja which works out the ideal level of parallelism.

This converts the GTK keyboard code to track the key down states of the lock modifiers NumLock and CapsLock so that they represent the actual "down" state of the key, rather than the lock state itself.

GTK tracks the lock state, and Flutter expects the down state.

autoninja is included as part of depot_tools and automatically
determines the optimal thread count.

Also applies quoting on the affected lines.

Cleans up header order/grouping for consistency: associated header, C/C++ system/standard library headers, library headers, platform-specific #includes.

Adds <cstring> where strlen, memcpy are being used: there are a bunch of places we use them transitively.

Applies linter-required cleanups. Disables linter on one file due to included RapidJson header. See https://github.com/flutter/flutter/issues/65676

This patch does not cover flutter/shell/platform/darwin. There's a separate, slightly more intensive cleanup for those in progress.