Some improvements:
- Fix or/xor chains (use left-associativity).
- Fix quote handling
- Make parsing O(n) rather than quadratic; limit recursion depth
And update tests.
Update various places for what we can do with C++20:
- ends_with / starts_with
- std::to_array
- using instead of typedef
- designated initializers
- "[[maybe_unused]]" instead of G_GNUC_UNUSED
Also remove some unnecessary 'static'
Only include xapian.h in one place, so we can have consistent options.
With that in place, we can enable C++ move semantics.
We don't do anything with that yet, but we check in the meson.build file
to see if we have the required xapian version.
Implement a new query parser; the results should be very similar to the
old one, but it adds an Sexp middle-representation, so users can see how
a query is interpreted.
