textfield height based only on clear text

Summary:
as the implicit height could change when switching to password mode,
use a textmetrics which always computes it from the visible text

BUG:399155

Test Plan: height doesn't change

Reviewers: #plasma, ngraham, rooty

Reviewed By: ngraham, rooty

Subscribers: sitter, rooty, ngraham, kde-frameworks-devel

Tags: #frameworks

Differential Revision: https://phabricator.kde.org/D19599

src/declarativeimports/plasmastyle/TextFieldStyle.qml

@@ -17,7 +17,7 @@
 *   51 Franklin Street, Fifth Floor, Boston, MA  2.010-1301, USA.
 */
 
-import QtQuick 2.0
+import QtQuick 2.6
 import QtQuick.Window 2.2
 import QtQuick.Controls 1.0
 import QtQuick.Controls.Styles 1.1 as QtQuickControlStyle
@@ -57,10 +57,17 @@ QtQuickControlStyle.TextFieldStyle {
 
         //In order to get the same height in both buttons and lineedits we need to apply the same rule here
 
-        implicitHeight: Math.max(control.cursorRectangle.height * 1.6, control.cursorRectangle.height + base.margins.top + base.margins.bottom)
+        implicitHeight: Math.max(metrics.height * 1.6,
+                                 metrics.height + base.margins.top + base.margins.bottom)
         implicitWidth: theme.mSize(theme.defaultFont).width * 12
         opacity: control.enabled ? 1 : 0.6
 
+        TextMetrics {
+            id: metrics
+            text: "M"
+            font: control.font
+        }
+
         Private.TextFieldFocus {
             id: hover
             state: control.activeFocus ? "focus" : (control.hovered ? "hover" : "hidden")