Revert "Fix drawing of collpsable insets"

This was definitely not meant to be pushed, especially since I
reverted it recently. Sorry folks.

This reverts commit 6fc72a1a1f.

src/insets/InsetCollapsable.cpp

@@ -335,10 +335,11 @@ void InsetCollapsable::draw(PainterInfo & pi, int x, int y) const
 			int w = 0;
 			int a = 0;
 			int d = 0;
+			Color const col = pi.full_repaint ? Color_none : pi.backgroundColor(this);
 			theFontMetrics(font).rectText(buttonLabel(bv), w, a, d);
 			int const ww = max(textdim.wid, w);
 			pi.pain.rectText(x + (ww - w) / 2, y + desc + a,
-			                 buttonLabel(bv), font, Color_none, Color_none);
+			                 buttonLabel(bv), font, col, Color_none);
 		}
 
 		int const y1 = y - textdim.asc + 3;

src/insets/InsetCollapsable.h

@@ -54,6 +54,8 @@ public:
 	void metrics(MetricsInfo &, Dimension &) const;
 	///
 	void draw(PainterInfo & pi, int x, int y) const;
+	///
+	virtual void drawBackground(PainterInfo &, int, int) const {}
 
 	/// return x,y of given position relative to the inset's baseline
 	void cursorPos(BufferView const & bv, CursorSlice const & sl,

src/insets/InsetText.cpp

@@ -221,6 +221,10 @@ void InsetText::draw(PainterInfo & pi, int x, int y) const
 	int const xframe = x + TEXT_TO_INSET_OFFSET / 2;
 	bool change_drawn = false;
 	if (drawFrame_ || pi.full_repaint) {
+		if (pi.full_repaint)
+			pi.pain.fillRectangle(xframe, yframe, w, h,
+				pi.backgroundColor(this));
+
 		// Change color of the frame in tracked changes, like for tabulars.
 		// Only do so if the color is not custom. But do so even if RowPainter
 		// handles the strike-through already.

src/insets/InsetText.h

@@ -60,6 +60,8 @@ public:
 	void metrics(MetricsInfo & mi, Dimension & dim) const;
 	///
 	void draw(PainterInfo & pi, int x, int y) const;
+	/// Drawing background is handled in draw
+	virtual void drawBackground(PainterInfo &, int, int) const {}
 	///
 	bool editable() const { return true; }
 	///