3.19.3 — Flutter - Product release notes & changelog tool

flutter/144565 - Fixes a tool crash when attempting to render a frame with raster stats on an application with the Impeller backend.
dart/55057 - Fixes an issue in dart2js where object literal constructors in interop extension types would fail to compile without an @JS annotation on the library.
dart/55095 - Disallows certain types involving extension types from being used as the operand of an await expression, unless the extension type itself implementsFuture.