Unsnap scrollable after snap_to operation

[tarkah]

When issuing a snap_to operation to a scrollable, it leaves it's offset "relative".

This is typically fine, except for when you use on_scroll / snap_to to keep 2 separate scrollables in "sync". For example, consider a table widget that has a separate header scrollable from it's body scrollable. We can keep the header in sync w/ the body by firing snap_to on the header from the body's on_scroll message. If you have "resizing" functionality setup on the columns of the table and you are horizontally scrolled and try to "resize" a column, the two scrollables now behave in opposite ways.

• The header which is at relative will stay x% scrolled as the width of the table changes, causing the viewport of the scrollable to change relative to the content.

• The body which is at absolute will stay scrolled at x regardless of the width changing, keeping the viewport static.

The behavior of always having an absolute offset stored is desired for when content width changes.

This fixes the issue by always "unsnapping" after offset changes from an operation.

[tarkah]

I just realized that snap_to is probably meant to keep things anchored at that percentage.

Maybe it'd be better to expose a scroll_to operation and have on_scroll transmit both the current relative and absolute offset to use for either?

[tarkah]

Closed in favor of #1796