[sources/path] Add gitignore-like pattern matching and warn on mismatches

Add gitignore-like pattern matching logic to `list_files()` and throw
warnings for paths getting different inclusion/exclusion results from
the old and the new methods.

Migration Tracking: <#4268>

Author: behnam

Cargo.lock

@@ -31,6 +31,7 @@ git2 = "0.6"
 git2-curl = "0.7"
 glob = "0.2"
 hex = "0.2"
+ignore = "^0.2.2"
 jobserver = "0.1.6"
 libc = "0.2"
 libgit2-sys = "0.6"

Cargo.toml

@@ -19,6 +19,7 @@ extern crate fs2;
 extern crate git2;
 extern crate glob;
 extern crate hex;
+extern crate ignore;
 extern crate jobserver;
 extern crate libc;
 extern crate libgit2_sys;