[3.10] bpo-46784: Add newly exported expat symbols to the namespace. (GH-31397) (GH-31420)

The libexpat 2.4.1 upgrade from  introduced the following new exported symbols:

* `testingAccountingGetCountBytesDirect`
* `testingAccountingGetCountBytesIndirect`
* `unsignedCharToPrintable`
* `XML_SetBillionLaughsAttackProtectionActivationThreshold`
* `XML_SetBillionLaughsAttackProtectionMaximumAmplification`

We need to adjust [Modules/expat/pyexpatns.h](https://github.com/python/cpython/blob/master/Modules/expat/pyexpatns.h)

(The newer libexpat upgrade  has no new symbols).

Automerge-Triggered-By: GH:gpshead
(cherry picked from commit 6312c1052c0186b4596fc45c42fd3ade9f8f5911)

Co-authored-by: Yilei "Dolee" Yang <yileiyang@google.com>

Co-authored-by: Yilei "Dolee" Yang <yileiyang@google.com>