move menu pages loader to Lua & add gui.load_document, file.ext(), file.prefix() & add core:gui_util module

res/modules/gui_util.lua

@@ -0,0 +1,38 @@
+local gui_util = {}
+
+--- Parse `pagename?arg1=value1&arg2=value2` queries
+--- @param query page query string
+--- @return page_name, args_table
+function gui_util.parse_query(query)
+    local args = {}
+    local name
+
+    local index = string.find(query, '?')
+    if index then
+        local argstr = string.sub(query, index + 1)
+        name = string.sub(query, 1, index - 1)
+        
+        local map = {}
+        for key, value in string.gmatch(argstr, "([^=&]*)=([^&]*)") do
+            map[key] = value
+        end
+        table.insert(args, map)
+    else
+        name = query
+    end
+    return name, args
+end
+
+--- @param query page query string
+--- @return document_id
+function gui_util.load_page(query)
+    local name, args = gui_util.parse_query(query)
+    local filename = file.find(string.format("layouts/pages/%s.xml", name))
+    if filename then
+        name = file.prefix(filename)..":pages/"..name
+        gui.load_document(filename, name, args)
+        return name
+    end
+end
+
+return gui_util