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`.

main/main.cpp

@@ -620,7 +620,7 @@ int Main::test_entrypoint(int argc, char *argv[], bool &tests_need_run) {
  * - setup(execpath, argc, argv, p_second_phase) is the main entry point for all platforms,
  *   responsible for the initialization of all low level singletons and core types, and parsing
  *   command line arguments to configure things accordingly.
- *   If p_second_phase is true, it will chain into setup2() (default behaviour). This is
+ *   If p_second_phase is true, it will chain into setup2() (default behavior). This is
  *   disabled on some platforms (Android, iOS, UWP) which trigger the second step in their
  *   own time.
  *