Fixes for bytearrays as hashmap key

[iamdefinitelyahuman]

What I did

Fix two compile-time issues related to bytearray types as HashMap keys:

• bytearrays that are part of a struct
• bytearrays in storage

Closes #2237

How I did it

1. In vyper/parser/parser_utils.py, do not assume that the key is a memory offset. This allows the use of structs.
2. In vyper/parser/expr.py, add a special case when the key is a bytearray in storage. Because sha3 only works on memory, we must first copy the bytearray to memory.

How to verify it

Run the tests. I've added several new cases to target this (and related) behavior.

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[codecov-io]

Codecov Report

Merging #2239 (c300fd8) into master (1a58196) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2239      +/-   ##
==========================================
+ Coverage   85.37%   85.38%   +0.01%     
==========================================
  Files          84       84              
  Lines        8566     8574       +8     
  Branches     2072     2074       +2     
==========================================
+ Hits         7313     7321       +8     
  Misses        746      746              
  Partials      507      507              

Impacted Files	Coverage Δ
vyper/parser/expr.py	77.82% <100.00%> (+0.22%)	⬆️
vyper/parser/parser_utils.py	81.42% <100.00%> (+0.14%)	⬆️

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