fix bytes20 literals

[charles-cooper]

What I did

fix #2780

also fix #2790 by blocking underscores in hex literals.

How I did it

propagate more type info down into codegen. note the bandaid in expr.py due to type annotations sometimes missing.

How to verify it

see tests

Commit message

Description for the changelog

Cute Animal Picture

[codecov-commenter]

Codecov Report

Merging #2782 (0cb1121) into master (fbed83c) will decrease coverage by 0.24%.
The diff coverage is 91.17%.

@@            Coverage Diff             @@
##           master    #2782      +/-   ##
==========================================
- Coverage   87.43%   87.18%   -0.25%     
==========================================
  Files          93       93              
  Lines        9939     9956      +17     
  Branches     2465     2424      -41     
==========================================
- Hits         8690     8680      -10     
- Misses        783      800      +17     
- Partials      466      476      +10     

Impacted Files	Coverage Δ
vyper/codegen/expr.py	80.73% <75.00%> (-0.33%)	⬇️
vyper/ast/nodes.py	94.20% <100.00%> (ø)
vyper/semantics/types/value/address.py	100.00% <100.00%> (+6.89%)	⬆️
vyper/semantics/types/value/bytes_fixed.py	100.00% <100.00%> (ø)
vyper/semantics/validation/annotation.py	92.15% <100.00%> (+0.21%)	⬆️
vyper/utils.py	87.27% <100.00%> (+0.15%)	⬆️
vyper/builtin_functions/convert.py	82.88% <0.00%> (-7.61%)	⬇️
vyper/ast/validation.py	68.88% <0.00%> (-4.45%)	⬇️
vyper/ir/s_expressions.py	91.17% <0.00%> (-2.95%)	⬇️
vyper/cli/vyper_json.py	79.42% <0.00%> (-0.37%)	⬇️
... and 4 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update fbed83c...0cb1121. Read the comment docs.