[BUG] Changing the length of a tween using the numeric input field (with keyboard) causes data loss as intermediate keyframes are thrown away

[nekohayo]

To Reproduce
Steps to reproduce the behavior:

1. Create a 15-frames-long tween with keyframes at frame no 1, 10
2. Click on the tween in the timeline
3. In the inspector sidebar, try to change the length from 15 to 25

Actual behavior
The keyframe at position 10 is lost because when you are typing the new length number, you first type the number "2" before typing number "5", and changes are instant-applied, so in practice it sets the length to 2 and discards any existing keyframe outside that boundary. This is data loss and is super dangerous UX.

Worse, if you click frame 10 and drag the existing item around to "recreate" the keyframe/movement, bug #357 happens!

Expected behavior
Do not ever throw away user data like that.

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Tested on Firefox directly on https://www.wickeditor.com/editor/