Fold hex into bytes

[iamdefinitelyahuman]

What I did

Before parsing the Vyper AST, fold hex values into bytes unless they are 20 or 32 bytes long (addresses or bytes32). This reduces some changes for ambiguity later when type checking.

How to verify it

Run the tests. I updated some tests that were failing.

Cute Animal Picture

[codecov-io]

Codecov Report

Merging #2191 into master will decrease coverage by 0.07%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2191      +/-   ##
==========================================
- Coverage   85.49%   85.42%   -0.08%     
==========================================
  Files          83       83              
  Lines        8503     8519      +16     
  Branches     2056     2060       +4     
==========================================
+ Hits         7270     7277       +7     
- Misses        729      736       +7     
- Partials      504      506       +2     

Impacted Files	Coverage Δ
vyper/ast/annotation.py	94.35% <100.00%> (+0.18%)	⬆️
vyper/context/types/value/array_value.py	91.89% <100.00%> (-0.11%)	⬇️
vyper/context/types/indexable/sequence.py	82.75% <0.00%> (-1.86%)	⬇️
vyper/functions/signatures.py	66.10% <0.00%> (-1.70%)	⬇️
vyper/functions/functions.py	89.33% <0.00%> (-0.40%)	⬇️
vyper/ast/nodes.py	93.46% <0.00%> (-0.39%)	⬇️
vyper/context/types/bases.py	89.06% <0.00%> (+0.08%)	⬆️
vyper/context/types/function.py	83.95% <0.00%> (+0.30%)	⬆️
vyper/context/types/meta/struct.py	80.32% <0.00%> (+1.01%)	⬆️

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