Make all names and fullnames into properties (#7829)
SymbolNode and FuncBase had name and fullname as methods while everything else has them as attributes or properties. Turn them into properties.
Fixes #7640.
This was done with `sed -i -e 's/\.name()/.name/g' -e 's/\.fullname()/.fullname/g' mypy/*.py mypy/*/*.py mypyc/*.py mypyc/*/*.py misc/proper_plugin.py test-data/unit/plugins/*.py`.
