pulseaudio: switch to git snapshot

pulseaudio: switch to git snapshot

The last release, 17.0, dates from January 2024. Master has since
accumulated fixes not available in any release, among them the SAP
port byte order in module-rtp-recv, an out-of-bounds access in
stream_get_timing_info_callback, multichannel processing in
module-echo-cancel and several JSON UTF-8 handling fixes. Switch to
the current master head.

The snapshot tarball carries neither a .git directory nor the
.tarball-version file of a release tarball, so git-version-gen has no
source for the version string and meson would fail parsing the empty
result. Write .tarball-version in Build/Prepare from the last release
tag reachable from the snapshot plus the abbreviated commit, so the
library version and the libpulsecommon file name derive from 17.0 as
the build's own git describe would.

Keep PKG_VERSION at 17.0 instead of the date-derived default, so the
package version matches what the libraries and binaries report, the
CI version check finds it in the --version output, and a later switch
back to a release tarball still sorts as an upgrade. PKG_SOURCE_DATE
and PKG_SOURCE_VERSION identify the snapshot, and the repacked tarball
carries both in its name so that a later snapshot does not collide with
this one in the download directory and on the source mirror.

Upstream turned the doxygen and tests options into feature options;
pass disabled instead of false. Normalise the indentation of the last
three MESON_ARGS entries while touching them.

Signed-off-by: Mirko Vogt <redacted>