Use StringBuilder where possible with DocumentUri

[david-driscoll]

Fixes #252

[codecov]

Codecov Report

Merging #339 into master will decrease coverage by 0.12%.
The diff coverage is 71.02%.

@@            Coverage Diff             @@
##           master     #339      +/-   ##
==========================================
- Coverage   75.30%   75.17%   -0.13%     
==========================================
  Files         427      428       +1     
  Lines       12434    12495      +61     
  Branches     1134     1146      +12     
==========================================
+ Hits         9363     9393      +30     
- Misses       3071     3102      +31     

Impacted Files	Coverage Δ
test/TestingUtils/Attributes.cs	40.38% <40.38%> (ø)
src/Protocol/DocumentUri.Internal.cs	95.28% <100.00%> (+0.16%)	⬆️
src/Server/DefaultLanguageServerFacade.cs	78.78% <100.00%> (-0.63%)	⬇️

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