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/CallbackTweener.xml

@@ -14,7 +14,8 @@
 			<return type="CallbackTweener" />
 			<param index="0" name="delay" type="float" />
 			<description>
-				Makes the callback call delayed by given time in seconds. Example:
+				Makes the callback call delayed by given time in seconds.
+				[b]Example:[/b]
 				[codeblock]
 				var tween = get_tree().create_tween()
 				tween.tween_callback(queue_free).set_delay(2) #this will call queue_free() after 2 seconds