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/PopupMenu.xml

@@ -526,15 +526,14 @@
 		<signal name="id_focused">
 			<param index="0" name="id" type="int" />
 			<description>
-				Emitted when user navigated to an item of some [param id] using [code]ui_up[/code] or [code]ui_down[/code] action.
+				Emitted when the user navigated to an item of some [param id] using the [member ProjectSettings.input/ui_up] or [member ProjectSettings.input/ui_down] input action.
 			</description>
 		</signal>
 		<signal name="id_pressed">
 			<param index="0" name="id" type="int" />
 			<description>
 				Emitted when an item of some [param id] is pressed or its accelerator is activated.
-
-				[b]Note:[/b] If [param id] is negative (either explicitly or due to overflow), this will return the correponding index instead.
+				[b]Note:[/b] If [param id] is negative (either explicitly or due to overflow), this will return the corresponding index instead.
 			</description>
 		</signal>
 		<signal name="index_pressed">