Style: Misc docs and comment style and language fixes

- Removed empty paragraphs in XML.
- Consistently use bold style for "Example:", on a new line.
- Fix usage of `[code]` when hyperlinks could be used (`[member]`, `[constant]`).
- Fix invalid usage of backticks for inline code in BBCode.
- Fix some American/British English spelling inconsistencies.
- Other minor fixes spotted along the way, including typo fixes with codespell.
- Don't specify `@GlobalScope` for `enum` and `constant`.

doc/classes/EditorInterface.xml

@@ -222,7 +222,7 @@
 		<method name="save_scene">
 			<return type="int" enum="Error" />
 			<description>
-				Saves the scene. Returns either [code]OK[/code] or [code]ERR_CANT_CREATE[/code] (see [@GlobalScope] constants).
+				Saves the scene. Returns either [constant OK] or [constant ERR_CANT_CREATE].
 			</description>
 		</method>
 		<method name="save_scene_as">