[web] Fix text selection from right to left

[mdebbar]

When the user uses a mouse to select text dragging from right to left, the selection keeps flickering, and copying doesn't work. (dragging from left to right works fine).

This was introduced in flutter/flutter#71756. The framework started allowing reverse base/extent offsets for selection. That throws off the <input>/<textarea> DOM element.

Fixes flutter/flutter#74504

[justinmc]

LGTM 👍

Thanks for fixing this. I knew I was going to break something when I started allowing reversed base/extent.

Is Flutter Web able to distinguish between selections made left-to-right vs. right-to-left? Or I'm guessing that part is handled by the browser and Flutter doesn't care which direction the selection was made from?

I'm talking about cases like this:

abc|def|g

Then shift + left arrow is pressed. If the selection was made with the mouse left to right then it will look like this:

abc|de|fg

But if it was made right to left then it would be:

ab|cdef|g

[mdebbar]

@justinmc the browser always uses base/extent in order. Even if you select from right to left, the browser doesn't revert base/extent. You can try it here: https://jsfiddle.net/ex736p81/2/

[justinmc]

Ah thanks, you're right! It must be keeping track of the direction or something like that elsewhere. Well I guess as long as the behavior is the same then it's all good.