cgi: various improvements (#3790)

- add max_num_fields to FieldStorage
- fix various types based on default values

tests/stubtest_whitelists/py35.txt

@@ -17,7 +17,6 @@ asyncio.runners
 asyncio.tasks.Task.__init__
 bdb.GENERATOR_AND_COROUTINE_FLAGS
 builtins.str.maketrans
-cgi.escape
 cmath.log
 codecs.StreamRecoder.seek
 collections.Reversible

tests/stubtest_whitelists/py36.txt

@@ -9,7 +9,6 @@ asyncio.protocols.BufferedProtocol
 asyncio.runners
 asyncio.tasks.Task._wakeup
 builtins.str.maketrans
-cgi.escape
 cmath.log
 codecs.StreamRecoder.seek
 collections.AsyncGenerator.ag_await

tests/stubtest_whitelists/py37.txt

@@ -22,7 +22,6 @@ asyncio.selector_events.BaseSelectorEventLoop.create_unix_server
 builtins.dict.get
 builtins.reversed
 builtins.str.maketrans
-cgi.escape
 cmath.log
 collections.AsyncGenerator.ag_await
 collections.AsyncGenerator.ag_code

tests/stubtest_whitelists/py3_common.txt

@@ -125,9 +125,6 @@ bz2.BZ2File.readinto
 bz2.BZ2File.readlines
 bz2.BZ2File.write
 bz2.BZ2File.writelines
-cgi.FieldStorage.__init__
-cgi.parse
-cgi.parse_header
 codecs.BufferedIncrementalDecoder.decode
 codecs.CodecInfo.decode
 codecs.CodecInfo.encode