Clean composing text when resetting the keyboard layout

PR#1104 enabled word autocompletion in latin keyboard. However it
also caused regressions like the following. Whenever there are multiple
text entries in a webpage, switching between them does not clear
the text used for autocompletion (the composing text) on time,
meaning that the content of the newly focused entry is filled in
with the text coming from the previously focused entry.

A way to fix that is by clearing the composing text whenever
resetKeyboardLayout is called.

Fixes #1177

app/src/common/shared/com/igalia/wolvic/ui/widgets/KeyboardWidget.java

@@ -455,6 +455,7 @@ private void resetKeyboardLayout() {
             mKeyboardView.setKeyboard(mCurrentKeyboard.getAlphabeticKeyboard());
         }
         handleShift(false);
+        cleanComposingText();
         updateCandidates();
     }