Added cgi.readData. Add test for cgi module. (#9645)

Added cgi.readData. Add test for cgi module.

tests/stdlib/tcgi.nim

@@ -0,0 +1,23 @@
+discard """
+  action: run
+  file: tcgi.nim
+  output: "[Suite] Test cgi module"
+"""
+
+import unittest
+import cgi, strtabs
+
+suite "Test cgi module":
+  const queryString = "foo=bar&фу=бар&checked=✓&list=1,2,3&with_space=text%20with%20space"
+
+  test "test query parsing with readData":
+    let parsedQuery = readData(queryString)
+
+    check parsedQuery["foo"] == "bar"
+    check parsedQuery["фу"] == "бар"
+    check parsedQuery["checked"] == "✓"
+    check parsedQuery["list"] == "1,2,3"
+    check parsedQuery["with_space"] == "text with space"
+
+    expect KeyError:
+      discard parsedQuery["not_existing_key"]