Add script to run monkeytype typing on test suite (#14440)

* The monkeytype script takes an optional argument to specify a test
  module or directory to run. Otherwise the whole test suite will run.
* Add monkeytype sqlite db to gitignore.

.gitignore

@@ -107,3 +107,6 @@ desktop.ini
 
 # Secrets
 .lokalise_token
+
+# monkeytype
+monkeytype.sqlite3

script/monkeytype

@@ -0,0 +1,25 @@
+#!/bin/sh
+# Run monkeytype on test suite or optionally on a test module or directory.
+
+# Stop on errors
+set -e
+
+cd "$(dirname "$0")/.."
+
+command -v pytest >/dev/null 2>&1 || {
+  echo >&2 "This script requires pytest but it's not installed." \
+    "Aborting. Try: pip install pytest"; exit 1; }
+
+command -v monkeytype >/dev/null 2>&1 || {
+  echo >&2 "This script requires monkeytype but it's not installed." \
+    "Aborting. Try: pip install monkeytype"; exit 1; }
+
+if [ $# -eq 0 ]
+  then
+    echo "Run monkeytype on test suite"
+    monkeytype run "`command -v pytest`"
+    exit
+fi
+
+echo "Run monkeytype on tests in $1"
+monkeytype run "`command -v pytest`" "$1"