22442 [web] Better structure to prepare for rich text measurement (cla: yes, platform-web)

22443 [web] Refactor _measureSubstring to better suit rich text measurement (cla: yes, platform-web)

22444 [web] Reuse the existing font string builer in TextStyle (cla: yes, platform-web)

22597 [web] Implement tilemode for gradient shaders. (cla: yes, platform-web)

22618 [web] Fix test failure on high dpi device (cla: yes, platform-web)

22622 [web] Optimize Matrix4.identity (cla: yes, perf: speed, platform-web)

22771 [web] Add new line break type (prohibited) (cla: yes, platform-web)