d3b6e4044d
This PR adds `String? identifier` to `SemanticsUpdateBuilder` (currently it's only available in the temproary `SemanticsUpdateBuilderNew` API. This is mainly targeted at https://github.com/flutter/flutter/issues/17988 Steps: part 1: [engine] add `SemanticsUpdateBuilderNew` https://github.com/flutter/engine/pull/47961 part 2: [flutter] use `SemanticsUpdateBuilderNew` https://github.com/flutter/flutter/pull/138331 **part 3: [engine] update `SemanticsUpdateBuilder` to be the same as `SemanticsUpdateBuilderNew`** <-- we are here part 4: [flutter] use (now updated) `SemanticsUpdateBuilder` again. part 5: [engine] remove `SemanticsBuilderNew`