Fix Return key events in LineEdit & TextEdit on Android

Depending on the device implementation, editor actions could be
received with different action ids or not at all for multi-line.

Added a parameter to virtual keyboards to properly handle single-line
and multi-line cases in all situations.

Single-line:
Input type set to text without multiline to make sure actions are sent.
IME options are set to DONE action to force action id consistency.

Multi-line:
Input type set to text and multiline to make sure enter triggers new lines.
Actions are disabled by the multiline flag, so '\n' characters are
handled in text changed callbacks.

core/bind/core_bind.h

@@ -256,7 +256,7 @@ public:
 	void dump_resources_to_file(const String &p_file);
 
 	bool has_virtual_keyboard() const;
-	void show_virtual_keyboard(const String &p_existing_text = "");
+	void show_virtual_keyboard(const String &p_existing_text = "", bool p_multiline = false);
 	void hide_virtual_keyboard();
 	int get_virtual_keyboard_height();