refactor: remove FunctionSignature

[tserg]

What I did

Refactoring PR that removes GlobalContext.parse_type() and consolidates FunctionSignature into ContractFunctionT, and moves FrameInfo and IR labels into a new FunctionIRInfo class.

Also removes dead code in IR generation
- parse_Name in vyper/codegen/stmt.py is never reachable because a statement can no longer be a standalone Name node. ~
~ - This was the original form of the equivalent function a while [back (https://github.com/vyperlang/vyper/blob/17bfed46411e2bc9aa47c88a784f068a59a09d9d/vyper/parser/stmt.py). Also removed code related to a single statement Name node being "vdb", which "vdb" file no longer exists in the repo.

How I did it

How to verify it

See tests

Commit message

refactor: remove `FunctionSignature`

This commit merges the old `FunctionSignature` with the newer
`ContractFunctionT` class. The old functionality has been subsumed under
`ContractFunctionT`. `ContractFunctionT` has additionally been
refactored for clarity; the new main fields are `positional_args` and
`keyword_args`, which improves on the old terminology of
`base_args`/`default_args` vs `min_arg_count`/`max_arg_count` and
improves the readability of downstream code.

this commit also
- removes the old codegen `parse_type()` functions
- simplifies codegen by removing the sigs dictionary from
  `vyper/codegen/context.py`
- simplifies the `lookup_internal_function` routine (now renamed to
  `_align_kwargs`)
- simplifies `vyper/codegen/module.py` by removing the sigs dictionaries
  and now instead relying on type annotations

Description for the changelog

Remove parse_type() and FunctionSignature

Cute Animal Picture

[codecov-commenter]

Codecov Report

Merging #3390 (37af37c) into master (f450cb1) will decrease coverage by 21.36%.
The diff coverage is 93.63%.

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@@             Coverage Diff             @@
##           master    #3390       +/-   ##
===========================================
- Coverage   89.05%   67.69%   -21.36%     
===========================================
  Files          86       84        -2     
  Lines       10792    10758       -34     
  Branches     2449     2451        +2     
===========================================
- Hits         9611     7283     -2328     
- Misses        781     2847     +2066     
- Partials      400      628      +228     

Impacted Files	Coverage Δ
vyper/builtins/_utils.py	0.00% <ø> (-100.00%)	⬇️
vyper/codegen/global_context.py	90.47% <ø> (-9.53%)	⬇️
vyper/ast/nodes.py	72.58% <80.00%> (-21.66%)	⬇️
vyper/compiler/output.py	37.50% <85.71%> (-53.60%)	⬇️
vyper/semantics/types/function.py	69.50% <88.88%> (-15.03%)	⬇️
vyper/codegen/self_call.py	96.07% <94.11%> (+0.42%)	⬆️
vyper/codegen/function_definitions/common.py	97.40% <96.42%> (-2.60%)	⬇️
vyper/ast/expansion.py	79.06% <100.00%> (-15.94%)	⬇️
vyper/builtins/_convert.py	39.69% <100.00%> (-51.18%)	⬇️
vyper/codegen/context.py	89.43% <100.00%> (-2.54%)	⬇️
... and 12 more

... and 39 files with indirect coverage changes

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[charles-cooper]

ah interesting - i was originally planning to remove FunctionSignature entirely and replace its functionality with ContractFunctionT, maybe that should be the scope of this PR instead?

[charles-cooper]

alright - i made a couple more changes that i had been planning to do later but seemed appropriate as part of this PR:

• remove the sigs data structure from the codegen Context object entirely
• remove the local_sigs dict from vyper/codegen/module.py, and
• lookup_internal_function into vyper/codegen/self_call.py

these clean up a lot of the conceptual burden around how function signatures are calculated and passed around, and lay some nice groundwork for future work on modules :)

[charles-cooper]

looks good, nice work!