Workaround bug with native rendering and opacity in TextField text

Summary:
Problem is identified in https://bugreports.qt.io/browse/QTBUG-70138
with a potential patch for upstream.

With native rendering the alpha is pointlessly also set in the
glBlendFunc despite also being used in the uniform of the shader.
Resulting in a visual bug when used on a window with alpha (such as
Dialog)

It sucks, but we were starting to see people work round it by copying
more invasive workarounds everywhere else which I want to avoid.

BUG: 396813

Test Plan: Looked at a text field

Reviewers: #plasma, broulik

Reviewed By: #plasma, broulik

Subscribers: ngraham, kde-frameworks-devel

Tags: #frameworks

Differential Revision: https://phabricator.kde.org/D15021

src/declarativeimports/plasmastyle/TextFieldStyle.qml

@@ -43,8 +43,12 @@ QtQuickControlStyle.TextFieldStyle {
      * Also if we are on mobile, make sure we use QtRendering
      * Finally, use QtRendering if we're using a non-integer scale factor to work around
      * https://bugreports.qt.io/browse/QTBUG-67007
+     *
+     * color with an alpha is also broken. https://bugreports.qt.io/browse/QTBUG-70138
+     *
+     * Given we have so many issues, just enable QtRendering for now
      */
-    renderType: !QtQuickControlsPrivate.Settings.isMobile && control.echoMode == TextInput.Normal && Screen.devicePixelRatio % 1 == 0 ? Text.NativeRendering : Text.QtRendering
+    renderType: Text.QtRendering
 
     background: Item {
         //QQC button heights are max(backgroundHeight, label + margins).