Remove mouse tap text drag selection throttling to improve responsiveness

[loune]

Currently, drag selecting text fields with a mouse in Flutter desktop and web feels sluggish, especially compared to platform native applications. This is due to the throttling of text selection updates with the aim of reducing excessive layout. This PR removes the drag selection throttling.

Since there is already logic which stops recalculating layout if the text is unchanged, the throttling on TextSelectionGestureDetector seems unneccesary. Also, text selection via other means such as drag handles on Android and iOS platforms does not have the throttle logic.

Here is a video of text selection before and after the PR:

text-select.mp4

Live Demo: https://flutter-apps-ll-public.s3.us-west-2.amazonaws.com/text-selection/index-frame.html

Related issue: #78908

Since this is removing code, I don't feel unit tests are neccessary but happy to be corrected.

Pre-launch Checklist

• I read the [Contributor Guide] and followed the process outlined there for submitting PRs.
• I read the [Tree Hygiene] wiki page, which explains my responsibilities.
• I read and followed the [Flutter Style Guide], including [Features we expect every widget to implement].
• I signed the [CLA].
• I listed at least one issue that this PR fixes in the description above.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is [test-exempt].
• All existing and new tests are passing.

[gspencergoog]

cc @justinmc

[justinmc]

Thank you for the PR @loune!

@mdebbar I think you originally added text selection throttling when using the mouse, can you comment on this idea to remove it?

It does feel much better to me without the throttling after trying it on web and Linux. I never noticed it was laggy before but now I can't unsee it...

[mdebbar]

LGTM!

I think the throttling was added when web's text layout was too slow. Things have changed since, so we can remove the throttling.

[mdebbar]

This is public API, which makes removing it a breaking change because some apps might be using it.

[gspencergoog]

Yes, this will need to be deprecated instead. You can start to ignore the value, but it needs to stay in the API for a while.

Check out other examples of deprecation in the code (search for "@deprecated"), and look at https://github.com/flutter/flutter/wiki/Tree-hygiene#deprecations

Be sure to update the documentation comment to make it obvious that the field is deprecated, and that it will be ignored.

[loune]

I wasn't aware TapAndDragGestureRecognizer could be used by other apps. If that's the case then perhaps we keep dragUpdateThrottleFrequency and just make the text_selection.dart changes?

[Renzo-Olivares]

@loune That sounds good to me. I think you can also remove the comments in tap_and_drag_gestures.dart related to this issue.

/// See also:
///   * [TextSelectionGestureDetector], which uses this parameter to avoid excessive updates
///     text layouts in text fields.

[Renzo-Olivares]

LGTM but Google testing is failing. I'll try to see what's happening there.

[Renzo-Olivares]

This is passing google testing (ran locally). Will merge once all the github tests are green.

[Renzo-Olivares]

This needs to be synced up to master again due to some recent changes in text_selection.dart .