internal/mcp/internal/util: add Wrapf

Add Wrapf, a function that helps with error wrapping.

Change-Id: I102695f75e4d217e09f828f4723cbfcbbe83f887
Reviewed-on: https://go-review.googlesource.com/c/tools/+/679177
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-by: Sam Thanawalla <samthanawalla@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

jsonschema/util.go

@@ -282,10 +282,3 @@ func assert(cond bool, msg string) {
 		panic("assertion failed: " + msg)
 	}
 }
-
-// wrapf wraps *errp with the given formatted message if *errp is not nil.
-func wrapf(errp *error, format string, args ...any) {
-	if *errp != nil {
-		*errp = fmt.Errorf("%s: %w", fmt.Sprintf(format, args...), *errp)
-	}
-}