libweston: Add surface-fps log scope

Add a 'surface-fps' log scope which will print out the current
frames per second for all surfaces on the fly.

This introduces a simple configuration in weston.ini:

[core]
surface-fps=true

The default value is false, so no behavioral change is introduced.
Status Job ID Name Coverage
  Container Prep
passed #780400
container_prep

00:00:19

 
  Build
passed #780401
build-native-meson

00:01:03