Convert tidy to a non-egg Python package

It seems that servo-tidy is only used by webrender in my GitHub
searches. WebRender could simply use `rustfmt` and the tidy on pypi
hasn't been updated since 2018. Converting tidy to a normal Python
package removes the maintenance burden of continually fixing the easy
install configuration.

Fixes #29094.
Fixes #29334.

python/tidy/tests/shell_tidy.sh

@@ -0,0 +1,14 @@
+#!/bin/bash
+#
+# Tests tidy for shell scripts.
+
+set -o nounset
+
+# Talking about some `concept in backticks` # shouldn't trigger
+echo "hello world"
+some_var=`echo "command substitution"`
+another_var="$some_var"
+if [ -z "${some_var}" ]; then
+  echo "should have used [["
+fi
+[ -z "${another_var}" ]