win-capture: Separate window finding source code

Because other capture methods may end up needing to share this code,
separate the window finding source code to window-helpers.c and
window-helpers.h.

This include a function to fill out a property list with windows, a
function to find a window based upon priority/title/class/exe, and a
function to decode the window title/class/exe strings from a window
setting string.

plugins/win-capture/window-helpers.h

@@ -0,0 +1,25 @@
+#pragma once
+
+enum window_priority {
+	WINDOW_PRIORITY_CLASS,
+	WINDOW_PRIORITY_TITLE,
+	WINDOW_PRIORITY_EXE,
+};
+
+enum window_search_mode {
+	INCLUDE_MINIMIZED,
+	EXCLUDE_MINIMIZED
+};
+
+extern void fill_window_list(obs_property_t *p, enum window_search_mode mode);
+
+extern void build_window_strings(const char *str,
+		char **class,
+		char **title,
+		char **exe);
+
+extern HWND find_window(enum window_search_mode mode,
+		enum window_priority priority,
+		const char *class,
+		const char *title,
+		const char *exe);