[C++] Add URI parsing facility

[asfimport]

This is a prerequisite for ARROW-4651.

Reporter: Antoine Pitrou / @pitrou
Assignee: Antoine Pitrou / @pitrou

Related issues:

• [Format] Flight Location should be more flexible than a (host, port) pair (Dependency)

PRs and other links:

• GitHub Pull Request #3779

_{Note: This issue was originally created as ARROW-4697. Please see the migration documentation for further details.}

[asfimport]

Antoine Pitrou / @pitrou:
Fixed by pull request #3779

[asfimport]

Uwe Korn / @xhochy:
Only resolve issues, don't close them. We need this during our release process.