Regex type with flags produces trailing slash in input props

[boylett]

The Problem

Using unstable_inputProps on a field with a regex string type that happens to have flags creates an invalid pattern property on the input.

CodeSandbox Link

The Solution

Rather than assuming all regular expressions don't have flags, we should either throw an error if they do, or sanitize them and remove the flags.

It would be ideal to add this detail to the documentation too, to ensure developers know that their flags will be ignored so that they can adjust their expressions accordingly.

./src/input-props.ts:53

        if (check.kind === "regex") {
-            props.pattern = check.regex.toString().slice(1, -1);
+            const str = check.regex.toString();
+            const del = str[ 0 ] || "/";
+            props.pattern = str.slice(1, str.lastIndexOf(del));
        }

Happy to make a pull request if necessary.