bpo-40334: Always show the caret on SyntaxErrors (GH-20050)

bpo-40334: Always show the caret on SyntaxErrors (GH-20050)

This commit fixes SyntaxError locations when the caret is not displayed,
by doing the following:

- `col_number` always gets set to the location of the offending
  node/expr. When no caret is to be displayed, this gets achieved
  by setting the object holding the error line to None.

- Introduce a new function `_PyPegen_raise_error_known_location`,
  which can be called, when an arbitrary `lineno`/`col_offset`
  needs to be passed. This function then gets used in the grammar
  (through some new macros and inline functions) so that SyntaxError
  locations of the new parser match that of the old.