refactor: reimplement AST folding

[tserg]

What I did

fixes #3363, #3344

How I did it

How to verify it

Commit message

refactor: reimplement AST folding

this commit reimplements AST folding. fundamentally, it changes AST
folding from a mutating pass to be an annotation pass. this brings
several benefits:
- typechecking is easier, because folding does not have to reason at all
  about types. type checking happens on both the folded and unfolded
  nodes, so intermediate values are type-checked.
- correctness in general is easier, because the AST is not mutated.
  there is also some incidental performance benefit, although that is
  not necessarily the focus here.
- the vyper frontend is now nearly mutation-free. only the getter AST
  expansion pass remains.

note that we cannot push folding past the typechecking stage entirely,
because some type checking operations depend on having folded values
(e.g., `range()` expressions, or type expressions with integer
parameters).

the approach taken in this commit is to change constant folding to be
annotating, rather than mutating. this way, type-checking can operate on
the original AST (and check for the folded values where needed).
intermediate values are also type-checked, so expressions like
`x: uint128 = 2**128 + 1 - 1` are caught by the typechecker.

summary of changes:
- `evaluate()` is renamed to `_try_fold()`. a new utility function
  called `get_folded_value()` caches folded values and is threaded
  through the codebase.
- `pre_typecheck` is added, which extracts `constant` variables and runs
  `get_folded_value()` on all nodes.
- a new `Modifiability` enum replaces the old (confusing) `is_constant`
  and `is_immutable` attributes on ExprInfo.
- `ExprInfo.is_transient` is removed, and handled by adding `TRANSIENT`
  to the `DataLocation` enum.
- the old `check_literal` and `check_kwargable` utility functions are
  replaced with a more general (and more correct) `check_modifiability`
  function
- several utility functions (ex. `_validate_numeric_bounds()`) related
  to ad-hoc type-checking (which would happen during constant folding)
  are removed.
- `CompilerData.vyper_module_folded` is renamed to
  `annotated_vyper_module`
- the AST output options are now `ast` and `annotated_ast`.
- `None` literals are now banned in AST validation instead of during
  analysis.

Description for the changelog

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[charles-cooper]

some of these tests should really go in tests/functional/builtins/folding/

[charles-cooper]

i think typically in computer science lore the next name in the list is QUX :D

[charles-cooper]

but i like BAX too tbh

[tserg]

i think typically in computer science lore the next name in the list is QUX :D

Oops I was not aware of this!

[charles-cooper]

nice work -- vyper is looking much cleaner now!

[charles-cooper]

@cyberthirst please take a look and see if you think there are any regressions in this PR as it's a bit large!