utilities: move package to public API

[johanbrandhorst]

This was made internal, but it's actually used
by the generated files.

[codecov-commenter]

Codecov Report

Merging #1395 into v2 will not change coverage.
The diff coverage is 0.00%.

@@           Coverage Diff           @@
##               v2    #1395   +/-   ##
=======================================
  Coverage   58.82%   58.82%           
=======================================
  Files          32       32           
  Lines        3891     3891           
=======================================
  Hits         2289     2289           
  Misses       1349     1349           
  Partials      253      253           

Impacted Files	Coverage Δ
internal/httprule/compile.go	100.00% <ø> (ø)
...-gen-grpc-gateway/internal/gengateway/generator.go	37.86% <0.00%> (ø)
...c-gen-grpc-gateway/internal/gengateway/template.go	79.79% <ø> (ø)
runtime/pattern.go	88.43% <ø> (ø)
runtime/query.go	65.19% <ø> (ø)
utilities/readerfactory.go	0.00% <ø> (ø)
utilities/trie.go	92.30% <ø> (ø)

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