[tracker] (36 commits) ...Merge branch 'wip/carlosg/portal' into 'master'

[Sam Thursfield <sthursfield src gnome org>]

Summary of changes:

  5d23e24... libtracker-data: Add support for graph/service control over (*)
  8d642e3... libtracker-data: Add support for CONSTRAINT query prologues (*)
  cdb2352... libtracker-data: Allow reducing set to the empty graph (*)
  7c816f1... libtracker-data: Remove dead code (*)
  94329a0... libtracker-data: Refactor find_graph() function (*)
  3dac05d... libtracker-data: Filter find_graph() by the given constrain (*)
  f4aa3ae... libtracker-data: Restrict all uses of tracker_triples to th (*)
  48bee50... libtracker-common: Add method to build dbus URI (*)
  643866e... libtracker-data: Implement DEFAULT/ALL in CONSTRAINT declar (*)
  3e7ec47... libtracker-data: Filter down updates on forbidden graphs (*)
  5b05052... libtracker-data: Check graph permissions on graph manipulat (*)
  22ebbfa... libtracker-data: Add graph policy checks on FTS queries (*)
  f72dac5... libtracker-sparql: Export DBus endpoint structs in private  (*)
  fe7736e... libtracker-sparql: Add private filtering methods to Tracker (*)
  ac3eeb8... build: restore dbus/systemd options (*)
  41017d1... portal: Add XDG portal implementation (*)
  1a1dd3c... portal: Implement filtering endpoint (*)
  f2f8833... libtracker-bus: Fallback through portal on bus connections (*)
  48811cc... examples: Add example flatpak definition (*)
  9c06e93... portal: Handle */default keywords in policy (*)
  cf7a5ff... portal: Set up watch on peers (*)
  69506ee... portal: Add DBus service file (*)
  160f706... docs: Add tracker3-xdg-portal manpage (*)
  edc8313... portal: Add CloseSession request (*)
  7d03185... libtracker-bus: Explicitly close sandbox sessions on connec (*)
  b1300c4... libtracker-data: Cache connections in SERVICES{} virtual ta (*)
  aa3e994... portal: Add systemd user session unit file (*)
  54f4281... portal: Handle missing .flatpak-info file (*)
  b3d3837... tests: Add tests for CONSTRAINT declarations in prologue (*)
  8a745e1... portal: Handle default object path in lookups (*)
  de9e671... ci: Don't install systemd user services (*)
  91feceb... libtracker-data: Allow prefixed names in constraint rules (*)
  dc30f02... portal: Allow prefixed names in graph constraints (*)
  97c0c7a... tracker: Initialize variable (*)
  ee166fa... libtracker-sparql: Allow NULL store in tracker_sparql_conne (*)
  df29906... Merge branch 'wip/carlosg/portal' into 'master'

(*) This commit already existed in another branch; no separate mail sent