Correct Folder View sizing and representation switch behavior

Summary:
* Resolve inherent layout hint conflicts between full and compact
  representations by setting them seperately.
  This fixes a recent regression causing tiny popups.
BUG:395477
* Correctly respect the panel icon size hint when scaling the
  compact representation, with the code and behavior now matching
  the Icon applet.
* Only expand into the full representation in place on vertical
  panels. This is not a bugfix, and optional. But I think the
  expansion is useless on horizontal panels, and this means fewer
  users have to care about changing the panel icon size hint if
  they're using a really tall horizontal panel or Latte with
  parabolic zooming.

Reviewers: mart, broulik, mvourlakos

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D13870