Non-controversial bits separated from #598.

This updates versions for the `revert` keyword (and the associated
statement, introduced in 0.8.4) and the `global` (introduced in 0.8.13
for the using directive) contextual keywords in both the new DSL and our
old YAML spec.

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Co-authored-by: Omar Tawfik <15987992+OmarTawfik@users.noreply.github.com>

Closes #568 

There is still one outstanding issue where we return a `Vec<TokenKind>`
from `next_token`; it'd like to return a more specialized type and
ideally pass it on stack (2x2 bytes), rather than on-heap (extra 3x8
bytes for the Vec handle + indirection). We should name it better and
properly show that we can return at most 2 token kinds (single token
kind or identifier + kw combo).

To do:
- [x] Return tokens from `next_token` via stack

Apart from that, I think this is a more correct approach than #598,
especially accounting for the new keyword definition format in DSL v2.

The main change is that we only check the keyword trie and additionally
the (newly introduced) compound keyword scanners only after the token
has been lexed as an identifier. For each context, we collect Identifier
scanners used by the keywords and attempt promotion there.

The existing lexing performance is not impacted from what I've seen when
running the sanctuary tests and I can verify (incl. CST tests) that we
now properly parse source that uses contextual keywords (e.g. `from`)
and that the compound keywords (e.g. `ufixedMxN`) are properly
versioned.

This adapts the existing `codegen_grammar` interface that's a leftover
from DSLv1; I did that to work on finishing #638; once this is merged
and we now properly parse contextual keywords, I'll move to clean it up
and reduce the parser codegen indirection (right now we go from v2 -> v1
model -> code generator -> Tera templates; it'd like to at least cut out
the v1 model and/or simplify visiting v2 from the existing
`CodeGenerator`).

Please excuse the WIP comments in the middle; the first and the last
ones should make sense when reviewing. I can simplify this a bit for
review, if needed.