Power user command support for directory scans (#467)

* Power-user directory source support
Signed-off-by: Mikey Strauss <mikey@scribe-security.com>

Signed-off-by: houdini91 <mdstrauss91@gmail.com>

* Remove newline

Signed-off-by: houdini91 <mdstrauss91@gmail.com>

* Shared filetree (#1)

* Shared directory resolver filetree

Signed-off-by: houdini91 <mdstrauss91@gmail.com>

* PR - change error ErrObserve to ErrPath

Signed-off-by: houdini91 <mdstrauss91@gmail.com>

* PR - share directory resolver
* Use pointer to source struct

Signed-off-by: houdini91 <mdstrauss91@gmail.com>

* Fix Lint

Signed-off-by: houdini91 <mdstrauss91@gmail.com>

syft/source/directory_resolver_test.go

@@ -178,9 +178,17 @@ func TestDirectoryResolverDoesNotIgnoreRelativeSystemPaths(t *testing.T) {
 	assert.Len(t, refs, 6)
 
 	// ensure that symlink indexing outside of root worked
-	assert.Contains(t, refs, Location{
-		RealPath: "test-fixtures/system_paths/outside_root/link_target/place",
-	})
+	ok := false
+	test_location := "test-fixtures/system_paths/outside_root/link_target/place"
+	for _, actual_loc := range refs {
+		if test_location == actual_loc.RealPath {
+			ok = true
+		}
+	}
+
+	if !ok {
+		t.Fatalf("could not find test location=%q", test_location)
+	}
 }
 
 func TestDirectoryResolverUsesPathFilterFunction(t *testing.T) {