revamp project assistant dialog

Use AdwWindow instead of deprecated GtkDialog, and GtkFileDialog
instead of deprecated GtkFileChooserNative.

Requires libadwaita >= 1.4
use N_() instead of __() to mark translatables
optimization: cache visible automation tracks
port some more deprecated Gtk widgets
remove unused RulerMarker code
export dialog: port GtkTreeView to GtkColumnView
fix header widget being focusable
stop using deprecated gtk_style_context_lookup_color()
fix various gtk depreciations
remove unused widget code
change audio effect icon in plugin browser
show focus ring on all focusable widgets
refactor channel send selector (use GtkListView)
cpu widget: add/remove sources on map/unmap (fixes crash), re-enable tooltip
implement cycling focus through panels with F6 and jumping to top with F10
move code from accel.c to zrythm_app.c
add focus ring on various widgets, make channel slot themable
fix allocating memory in dsp threads when recording automation

Also make the logic faster by reducing searches.
build: build some external projects with full optimization
remove height requirement for channel plugin slots/sends expanders