Improved for loop TypeMismatch exception

[iamdefinitelyahuman]

What I did

Improve exception on a failed for loop type check.

How I did it

When the target value in a for loop has multiple potential types, and using each type creates a different TypeMismatch, display all of the exceptions with an explanation as to what happened.

To do so, I've modified the nodes member of VyperException to be called annotations - it can now also be given as a tuple of ("message", node). This lets us attach specific messages to each annotation. I think there will be other places this is useful in the future.

How to verify it

Run tests.

Cute Animal Picture

[codecov-commenter]

Codecov Report

Merging #2119 into master will decrease coverage by 1.20%.
The diff coverage is 73.07%.

@@            Coverage Diff             @@
##           master    #2119      +/-   ##
==========================================
- Coverage   85.01%   83.81%   -1.21%     
==========================================
  Files          83       83              
  Lines        8288     8234      -54     
  Branches     2001     2002       +1     
==========================================
- Hits         7046     6901     -145     
- Misses        743      833      +90     
- Partials      499      500       +1     

Impacted Files	Coverage Δ
vyper/context/validation/local.py	88.38% <40.00%> (-0.70%)	⬇️
vyper/exceptions.py	93.51% <80.95%> (-2.56%)	⬇️
vyper/ast/annotation.py	85.96% <0.00%> (-7.90%)	⬇️
vyper/context/types/value/numeric.py	77.50% <0.00%> (-6.65%)	⬇️
vyper/functions/functions.py	83.83% <0.00%> (-5.88%)	⬇️
vyper/parser/expr.py	71.54% <0.00%> (-5.22%)	⬇️
vyper/ast/nodes.py	92.00% <0.00%> (-1.66%)	⬇️
vyper/functions/convert.py	73.46% <0.00%> (-1.37%)	⬇️
vyper/functions/signatures.py	67.24% <0.00%> (-0.56%)	⬇️
vyper/parser/context.py	90.80% <0.00%> (-0.41%)	⬇️
... and 8 more

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