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.
Xapian supports an "ngrams" option to help with languages/scripts
without explicit wordbreaks, such as Chinese / Japanese / Korean.
Add some plumbing for supporting this in mu as well. Experimental for
now.
When passing messages to mu, often we got a (parsed from string)
message-sexp from the message document; then appended some more
properties ("build_message_sexp").
Instead, we can do it in terms of the strings; this is _a little_
inelegant, but also much faster; compare:
(base)
[mu4e] Found 500 matching messages; 0 hidden; search: 1298.0 ms (2.60 ms/msg); render: 642.1 ms (1.28 ms/msg)
(with temp-file optimization (earlier commit)
[mu4e] Found 500 matching messages; 0 hidden; search: 1152.7 ms (2.31 ms/msg); render: 270.1 ms (0.54 ms/msg)
(with temp file optimize _and_ the string opt (this commit)
[mu4e] Found 500 matching messages; 0 hidden; search: 266.0 ms (0.53 ms/msg); render: 199.7 ms (0.40 ms/msg)
This makes queries where we don't need the sexp much faster; e.g.
before:
mu find "a" --include-related 47,51s user 2,68s system 99% cpu 50,651 total
after:
mu find "a" --include-related 7,12s user 1,97s system 87% cpu 10,363 total
