vega: Escape special characters in field and title.

[daavoo]

Closes #80

[codecov-commenter]

Codecov Report

Base: 95.79% // Head: 95.91% // Increases project coverage by +0.12% 🎉

Coverage data is based on head (5731117) compared to base (c6f6abc).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #81      +/-   ##
==========================================
+ Coverage   95.79%   95.91%   +0.12%     
==========================================
  Files          19       19              
  Lines         642      661      +19     
  Branches      119      121       +2     
==========================================
+ Hits          615      634      +19     
  Misses         22       22              
  Partials        5        5              

Impacted Files	Coverage Δ
src/dvc_render/vega.py	97.29% <100.00%> (+0.03%)	⬆️
src/dvc_render/vega_templates.py	98.16% <100.00%> (+0.08%)	⬆️
tests/test_templates.py	100.00% <100.00%> (ø)
tests/test_vega.py	100.00% <100.00%> (ø)

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