Move tracking the number of touch sequences to ClutterInputDevice

Move the tracking of the number of touch sequences on the screen to
determine whether the sequence is pointer emulating from
MetaGestureTracker to ClutterInputDevice. To do this, add new API to get
the number of touches to ClutterInputDevice and remove the API from
MetaGestureTracker.

This is a first step for removing the sequence tracking inside
meta-gesture-tracker, also it makes the check more clear since we can
compare the number against 1 now (the number of sequences of the input
device is already updated at this point).

GNOME/mutter!790
5 jobs for !790 with move-n-sequences-to-input-device in 2 minutes and 37 seconds (queued for 1 second)
latest detached
Status Job ID Name Coverage
  Review
passed #427503
check-commit-log

00:00:30

 
  Build
passed #427504
build-mutter

00:02:06

failed #427505
build-without-native-backend

00:01:14

 
  Test
skipped #427507
can-build-gnome-shell
skipped #427506
test-mutter
 
Name Stage Failure
failed
build-without-native-backend Build
[517/1370] Compiling C object 'src/25a6634@@mutter-5@sha/core_prefs.c.o'.
[518/1370] Compiling C object 'src/25a6634@@mutter-5@sha/core_startup-notification.c.o'.
[519/1370] Compiling C object 'src/25a6634@@mutter-5@sha/core_display.c.o'.
[520/1370] Compiling C object 'src/25a6634@@mutter-5@sha/core_stack.c.o'.
[521/1370] Compiling C object 'src/25a6634@@mutter-5@sha/ui_theme.c.o'.
[522/1370] Compiling C object 'src/25a6634@@mutter-5@sha/core_workspace.c.o'.
[523/1370] Compiling C object 'src/25a6634@@mutter-5@sha/ui_frames.c.o'.
ninja: build stopped: subcommand failed.
ERROR: Job failed: exit code 1