bake(cli): allow passing in-stream using command.Cli

ReadLocalFiles should allow passing the stdin file as an argument, which
allows us to read from dockerCli.Stdin() to be consistent with other
commands in the same package.

Signed-off-by: Justin Chadwell <me@jedevc.com>

bake/bake_test.go

@@ -1398,7 +1398,7 @@ func TestReadLocalFilesDefault(t *testing.T) {
 			for _, tf := range tt.filenames {
 				require.NoError(t, os.WriteFile(tf, []byte(tf), 0644))
 			}
-			files, err := ReadLocalFiles(nil)
+			files, err := ReadLocalFiles(nil, nil)
 			require.NoError(t, err)
 			if len(files) == 0 {
 				require.Equal(t, len(tt.expected), len(files))