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/ImporterMesh.xml

@@ -5,7 +5,6 @@
 	</brief_description>
 	<description>
 		ImporterMesh is a type of [Resource] analogous to [ArrayMesh]. It contains vertex array-based geometry, divided in [i]surfaces[/i]. Each surface contains a completely separate array and a material used to draw it. Design wise, a mesh with multiple surfaces is preferred to a single surface, because objects created in 3D editing software commonly contain multiple materials.
-
 		Unlike its runtime counterpart, [ImporterMesh] contains mesh data before various import steps, such as lod and shadow mesh generation, have taken place. Modify surface data by calling [method clear], followed by [method add_surface] for each surface.
 	</description>
 	<tutorials>