Toolbutton: Fix layout issues

- Improve spacing between icon and text
- Do not enforce a minimum width

Having a minimum width does not make much sense for a ToolButton:
1. It should aim at using the minimum amount of horizontal space when
   used in a ToolBar.
2. It looks unbalanced when used with an icon because the content is
   flushed to the left, leaving a large amount of white-space on the right.

REVIEW: 104735

declarativeimports/plasmacomponents/qml/ToolButton.qml

@@ -84,7 +84,7 @@ Item {
         if (label.paintedWidth == 0) {
             return implicitHeight
         } else {
-            return Math.max(theme.defaultFont.mSize.width*12, icon.width + label.paintedWidth + surface.margins.left + surface.margins.right) + ((icon.valid) ? surface.margins.left : 0)
+            return icon.width + label.paintedWidth + surface.margins.left + surface.margins.right + ((icon.valid) ? surface.margins.left : 0)
         }
     }
     implicitHeight: Math.max(theme.defaultFont.mSize.height*1.6, Math.max(icon.height, label.paintedHeight) + surface.margins.top/2 + surface.margins.bottom/2)
@@ -200,7 +200,7 @@ Item {
                 top: parent.top
                 bottom: parent.bottom
                 left: icon.valid ? icon.right : parent.left
-                leftMargin: icon.valid ? parent.anchors.leftMargin : 0
+                leftMargin: icon.valid ? surface.margins.left : 0
                 right: parent.right
             }
             font.capitalization: theme.defaultFont.capitalization