core: Move type parsing to lexer (NFC)

[math-fehr]

This moves the parsing of types to the lexer, from the tokenizer.
It does not change any functionality.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (main@c744c8c). Click here to learn what that means.
Patch coverage: 96.05% of modified lines in pull request are covered.

❗ Current head ee42088 differs from pull request most recent head 47eaa60. Consider uploading reports for the commit 47eaa60 to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1068   +/-   ##
=======================================
  Coverage        ?   86.79%           
=======================================
  Files           ?      130           
  Lines           ?    20442           
  Branches        ?     3098           
=======================================
  Hits            ?    17742           
  Misses          ?     2190           
  Partials        ?      510           

Impacted Files	Coverage Δ
xdsl/parser.py	85.34% <95.71%> (ø)
xdsl/dialects/func.py	95.75% <100.00%> (ø)

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