Fix #8971: Resize QueryStrings with interface scale change. (#10281)

* Fix: Use width of caret symbol '_' for text entry.

This replaces an arbitrary pixel width with the space actually required.

* Fix #8971: Update QueryString sizes with interface scale change.

src/window_gui.h

@@ -276,6 +276,7 @@ public:
 
 	const QueryString *GetQueryString(uint widnum) const;
 	QueryString *GetQueryString(uint widnum);
+	void UpdateQueryStringSize();
 
 	virtual const char *GetFocusedText() const;
 	virtual const char *GetCaret() const;