3252 [url_launcher] Update readme for URL schemes on iOS (cla: yes, p: url_launcher, waiting for tree to go green)

3333 [url_launcher] Fix PlatformException introduced in nnbd release (cla: yes, nnbd, p: url_launcher)

3475 [url_launcher] Update result to True when the url was loaded successfully. (cla: yes, p: url_launcher, platform-ios)

3476 [url_launcher_web] Fix Link misalignment issue (cla: yes, p: url_launcher)