modalTextEdit: hide placeholder when selected

GitLab: #986
Change-Id: I4672ca2240a04a2a25780506750d0233b442aba5

src/app/commoncomponents/MaterialTextField.qml

@@ -50,6 +50,7 @@ TextField {
     placeholderTextColor: !isActive
                           ? JamiTheme.transparentColor
                           : JamiTheme.placeholderTextColor
+    property string initialPlaceholderText
 
     property alias infoTipText: infoTip.text
 
@@ -105,7 +106,7 @@ TextField {
         font.pointSize: root.font.pointSize
         anchors.baseline: root.baseline
         anchors.horizontalCenter: root.horizontalCenter
-        text: root.placeholderText
+        text: root.initialPlaceholderText
         color: root.baseColor
         visible: !root.isActive && !readOnly && root.text.toString() === ""
     }
@@ -146,7 +147,7 @@ TextField {
         font.pointSize: root.font.pointSize - 3
         anchors.top: baselineLine.bottom
         anchors.topMargin: 2
-        text: root.placeholderText
+        text: root.initialPlaceholderText
         color: root.baseColor
 
         // Show the alternate placeholder while the user types.

src/app/commoncomponents/ModalTextEdit.qml

@@ -92,7 +92,7 @@ Loader {
             font.pointSize: root.fontPointSize
             font.bold: root.fontBold
             echoMode: root.echoMode
-            placeholderText: root.placeholderText
+            initialPlaceholderText: root.placeholderText
             onAccepted: root.accepted()
             onTextChanged: dynamicText = text
             text: staticText