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/JSON.xml

@@ -54,7 +54,7 @@
 			<param index="0" name="json_string" type="String" />
 			<description>
 				Attempts to parse the [param json_string] provided.
-				Returns an [enum Error]. If the parse was successful, it returns [code]OK[/code] and the result can be retrieved using [member data]. If unsuccessful, use [method get_error_line] and [method get_error_message] for identifying the source of the failure.
+				Returns an [enum Error]. If the parse was successful, it returns [constant OK] and the result can be retrieved using [member data]. If unsuccessful, use [method get_error_line] and [method get_error_message] for identifying the source of the failure.
 				Non-static variant of [method parse_string], if you want custom error handling.
 			</description>
 		</method>