src/qml/controls/subtitletext: fix misaligned subtitles

Use anchors for positioning to fix a rare issue where text could come
desynced from the stroke layer. This could happen because the top layer
would be drawn before the lower layer since Shape is asynchronous. Is it
rare transient issue, so this isn't a serious, but it should be fixed.
Since anchors update positions in response to geometery changes, this
should keep text aligned.

Author: ripose-jp

src/qml/controls/StrokeLabel.qml

@@ -59,6 +59,7 @@ Item {
 
                 Shape {
                     id: strokeShape
+                    anchors.centerIn: parent
                     antialiasing: true
                     layer.enabled: true
                     layer.samples: 8
@@ -84,8 +85,7 @@ Item {
 
                 Shape {
                     id: textShape
-                    x: root.margin
-                    y: root.margin
+                    anchors.centerIn: strokeShape
                     antialiasing: true
                     layer.enabled: true
                     layer.samples: 8

src/qml/controls/SubtitleText.qml

@@ -130,6 +130,7 @@ Item {
 
                 Shape {
                     id: strokeShape
+                    anchors.centerIn: parent
                     antialiasing: true
                     layer.enabled: true
                     layer.samples: 8
@@ -188,8 +189,7 @@ Item {
 
                 Shape {
                     id: textShape
-                    x: root.margin
-                    y: root.margin
+                    anchors.centerIn: strokeShape
                     antialiasing: true
                     layer.enabled: true
                     layer.samples: 8