Fix include paths in libtxt to prepare for upcoming Skia build change (#8723)

* Fix include paths in libtxt to prepare for upcoming Skia build change

Red test results are due to a different change. This PR fixes compile issues on the Skia side, and ensures that the next Skia -> Flutter roll can land properly.

third_party/txt/src/txt/font_skia.cc

@@ -15,7 +15,7 @@
  */
 
 #include "font_skia.h"
-#include "SkFont.h"
+#include "third_party/skia/include/core/SkFont.h"
 
 #include <minikin/MinikinFont.h>
 

third_party/txt/src/txt/font_skia.h

@@ -14,10 +14,10 @@
  * limitations under the License.
  */
 
-#include <SkPaint.h>
-#include <SkTypeface.h>
 #include <minikin/MinikinFont.h>
 #include "flutter/fml/macros.h"
+#include "third_party/skia/include/core/SkPaint.h"
+#include "third_party/skia/include/core/SkTypeface.h"
 
 namespace txt {