This restores the pre-PHP 8.1 behavior, where values of
static variables within inherited methods were independent
of each other. With PHP 8.1, this was changed to be truly
'static', which causes problems when one derivate of
PhabricatorLiskDAO defines a custom serializer but another
does not.
This came to light in T15726, but only for the Fund application,
which is a prototype, and deprecated. This fixes Fund, but
more importantly, everything else that would be broken by
this, whatever it was.
Ref: https://wiki.php.net/rfc/static_variable_inheritance
Previous stacktrace:
```
EXCEPTION: (RuntimeException) Undefined array key "totalAsCurrency" at [<arcanist>/src/error/PhutilErrorHandler.php:273]
#0 <#2> PhutilErrorHandler::handleError(integer, string, string, integer) called at [<phorge>/src/infrastructure/storage/lisk/PhabricatorLiskDAO.php:345]
#1 <#2> PhabricatorLiskDAO::willWriteData(array) called at [<phorge>/src/infrastructure/storage/lisk/LiskDAO.php:1085]
#2 <#2> LiskDAO::insertRecordIntoDatabase(string) called at [<phorge>/src/infrastructure/storage/lisk/LiskDAO.php:958]
#3 <#2> LiskDAO::insert() called at [<phorge>/src/infrastructure/storage/lisk/LiskDAO.php:927]
#4 <#2> LiskDAO::save() called at [<phorge>/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php:1405]
[...]
```