[lock/login screens] Focus password field after virtual keyboard appears

Without this, the virtual keyboard appears and takes focus, which
doesn't make sense:the password field needs to retain focus or else
the keystrokes you type using the virtual keyboard get eaten.

BUG: 430209
FIXED-IN: 5.21

lookandfeel/contents/lockscreen/LockScreenUi.qml

@@ -328,6 +328,9 @@ PlasmaCore.ColorScope {
             onKeyboardActiveChanged: {
                 if (keyboardActive) {
                     state = "visible";
+                    // Otherwise the password field loses focus and virtual keyboard
+                    // keystrokes get eaten
+                    mainBlock.mainPasswordBox.forceActiveFocus();
                 } else {
                     state = "hidden";
                 }

sddm-theme/Main.qml

@@ -258,6 +258,9 @@ PlasmaCore.ColorScope {
             onKeyboardActiveChanged: {
                 if (keyboardActive) {
                     state = "visible"
+                    // Otherwise the password field loses focus and virtual keyboard
+                    // keystrokes get eaten
+                    userListComponent.mainPasswordBox.forceActiveFocus();
                 } else {
                     state = "hidden";
                 }