Separate highlighting for warning, information and hint diagnostics

[mispencer]

PR Prelude

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Why this change is necessary and useful

Currently, there are two types of diagnostics highlighting: errors and everything else (effectively as warnings).

These changes adds two new highlighting for information and hint diagnostics, and provides sensible default for their highlighting and sign.

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This change is 

[codecov]

Codecov Report

Attention: Patch coverage is 88.00000% with 12 lines in your changes missing coverage. Please review.

Project coverage is 89.83%. Comparing base (131b182) to head (1a791f8).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4301      +/-   ##
==========================================
- Coverage   89.88%   89.83%   -0.05%     
==========================================
  Files          37       37              
  Lines        4763     4861      +98     
==========================================
+ Hits         4281     4367      +86     
- Misses        482      494      +12     

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