add "metadata" output format

[charles-cooper]

What I did

This commit adds a "metadata" output format which is intended to be
useful for downstream tooling. Right now it is limited to function
signatures and their metadata, but it could be extended to more metadata
about modules such as type definitions and in-scope interfaces
(basically everything in GlobalContext).

How I did it

How to verify it

# tmp/foo.vy
@internal
def foo() -> (uint256, uint256, uint256):
    return 1, 2, 3

@internal
def bar():
    pass

@external
def baz():
    self.foo()
    self.bar()

$ vyper -f metadata tmp/foo.vy
/home/charles/.venvs/vyper/lib/python3.8/site-packages/vyper-0.3.2+commit.b77ab184-py3.8.egg/vyper/compiler/output.py:93: UserWarning: metadata output format is unstable!
  warnings.warn("metadata output format is unstable!")
{"function_signatures": {"foo": {"name": "foo", "args": [], "return_type": "(uint256, uint256, uint256)", "mutability": "nonpayable", "internal": true, "nonreentrant_key": null, "is_from_json": false, "base_args": [], "default_args": [], "default_values": {}, "frame_start": 224, "frame_size": 0, "_lll_identifier": "internal_foo___"}, "bar": {"name": "bar", "args": [], "return_type": "None", "mutability": "nonpayable", "internal": true, "nonreentrant_key": null, "is_from_json": false, "base_args": [], "default_args": [], "default_values": {}, "frame_start": 224, "frame_size": 0, "_lll_identifier": "internal_bar___"}, "baz": {"name": "baz", "args": [], "return_type": "None", "mutability": "nonpayable", "internal": false, "nonreentrant_key": null, "is_from_json": false, "base_args": [], "default_args": [], "default_values": {}, "frame_start": 224, "frame_size": 96}}}

Description for the changelog

Cute Animal Picture

[codecov-commenter]

Codecov Report

Merging #2597 (74938a5) into master (23ed82c) will increase coverage by 0.38%.
The diff coverage is 84.83%.

@@            Coverage Diff             @@
##           master    #2597      +/-   ##
==========================================
+ Coverage   86.26%   86.64%   +0.38%     
==========================================
  Files          90       91       +1     
  Lines        9351     9430      +79     
  Branches     2370     2357      -13     
==========================================
+ Hits         8067     8171     +104     
+ Misses        796      774      -22     
+ Partials      488      485       -3     

Impacted Files	Coverage Δ
vyper/builtin_functions/utils.py	100.00% <ø> (ø)
vyper/codegen/stmt.py	86.61% <ø> (ø)
vyper/compiler/__init__.py	87.17% <ø> (ø)
vyper/utils.py	87.23% <ø> (+3.79%)	⬆️
vyper/codegen/expr.py	80.62% <50.00%> (+0.03%)	⬆️
vyper/semantics/types/user/interface.py	81.57% <75.00%> (-0.41%)	⬇️
vyper/codegen/types/types.py	84.92% <78.12%> (+1.58%)	⬆️
vyper/semantics/types/bases.py	83.95% <80.00%> (-0.20%)	⬇️
vyper/abi_types.py	80.95% <80.95%> (ø)
vyper/compiler/phases.py	92.52% <81.81%> (-1.54%)	⬇️
... and 28 more

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[lgtm-com]

This pull request fixes 2 alerts when merging b77ab18 into 23ed82c - view on LGTM.com

fixed alerts:

• 1 for Unused local variable
• 1 for Module is imported with 'import' and 'import from'