pgfmath: reset " catcode inside parser

[hmenke]

Motivation for this change

Fixes #1062

This will prevent the use of babel hyphens in pgfmath quoted text, but I'm pretty sure that this is a very niche use-case. See also discussion in the issue thread.

Checklist

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• Code changes are licensed under GPLv2 + LPPLv1.3c
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[muzimuzhi]

This won't fix use cases when the math expression is already tokenized before being parsed by pgfmath, hence I doubt if this really "fixes" #1062.

To allow an active quote as operator, more tricks are needed.

[hmenke]

@muzimuzhi I've update the approach. Now the parser is scanning for active ", but I wonder whether we have to generalize this for all the other special characters as well. Maybe a catcode-agnostic string comparison would be more appropriate in most places. This, however, will require some large refactoring and we should wait with this until we have the testsuite running.

[hmenke]

Superseded by #1073