manual: update the note about reserved attributes
manual: many fixes

Mostly around attributes and language items.
etc: attempts at fixing editor highlighting for new attribute syntax
manual: update style
manual: fix attribute ebnf
manual: further attribute clarifications

- Sort attributes lexicographically
- Use new attribute syntax consistently
- Fix wording describing new attribute syntax
- Expand section on `repr`
manual: refine ECMA-335 reference for attributes
auto merge of #13207 : cmr/rust/attrib-reference, r=kballard