Matching in genqlient by Normalizing Paths (#373)

This pull request addresses an issue with the `genqlient` library, which
uses the `doublestar` package for path matching. The current
implementation does not correctly match paths on Windows systems due to
differences in path separators. I've implemented a simple fix by
converting Windows-style backslashes (`\`) to forward slashes (`/`)
before performing the match, allowing the path matching to work
correctly across all platforms.

#371
bmatcuk/doublestar#61

Author: imbytecat

generate/parse.go

@@ -91,6 +91,8 @@ func expandFilenames(globs []string) ([]string, error) {
 	for _, glob := range globs {
 		// SplitPattern in case the path is absolute or something; a valid path
 		// isn't necessarily a valid glob-pattern.
+		glob = filepath.Clean(glob)
+		glob = filepath.ToSlash(glob)
 		base, pattern := doublestar.SplitPattern(glob)
 		matches, err := doublestar.Glob(os.DirFS(base), pattern, doublestar.WithFilesOnly())
 		if err != nil {