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This CL translates the path-to-regexp parser from typescript to c++.
Its based on the code here:

https://github.com/pillarjs/path-to-regexp/blob/125c43e6481f68cc771a5af22b914acdb8c5ba1f/src/index.ts#L126-L232

We deviate from the path-to-regexp code in some terminology and output
structure.  In particular, we output a list of Part structures with
types of kFixed, kRegex, kSegmentWildcard, or kFullWildcard as discussed
in the design doc:

https://docs.google.com/document/d/17L6b3zlTHtyxQvOAvbK55gQOi5rrJLERwjt_sKXpzqc/edit#heading=h.ymw6rim68920

Note, this CL does deviate from the design doc as well in that we are
translating a more modern version of path-to-regexp than originally
planned.  This uses a "{...}?" style grouping for applying modifiers.
We also do not yet fully include support for the "*" wildcard character.
As such the grammar in the design doc does not really apply fully to
this CL.

Bug: 1141510
Change-Id: I1c3e4ef76587496301d2171fa9f76b51754dce0d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2518206
Commit-Queue: Ben Kelly <wanderview@chromium.org>
Reviewed-by: Jeremy Roman <jbroman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#826968}