TextArea: prevent changing size of background recursively

When the x/y position of background depends on the height/width of
background and these values are not constant, the if statement in
the method resizeBackground() will always pass. And since
`resizingBackground` guard wasn't checked, any geometry change
will always call resizeBackground() and then call
themself recursively (via the change listener),
that means the height/width of background will
always be reset, no matter what value you set.
Another part of the issue was in determining the extra bits too late:
in case the background gets parented by the flickable, the new child
caused the flickable to re-calculate its metrics and thus resize
the background *prior* to remembering if it has w/h set.

As a side effect, this fix also brings the possibility to reset
previously set w/h to get the default background sizing behavior.

Inspired by da06da57002b64cf4bcde0ca708b3275a5f919ae

[ChangeLog][QtQuick][QQuickTextArea] prevent changing size
of background recursively in construction

Fixes: QTBUG-76369
Change-Id: Ide51ec1ebab63605ae3bfcc10a76a28be960ef36
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>

0 files changed, 0 insertions, 0 deletions