sm.puri.Squeekboard.desktop: make path to Exec= absolute

This uses the same logic from Phosh to render absolute paths in .desktop
files.

data/meson.build

@@ -7,13 +7,20 @@ squeekboard_resources = gnome.compile_resources(
    c_name: 'squeekboard',
 )
 
+desktopconf = configuration_data()
+desktopconf.set('bindir', bindir)
+
 desktop_file = 'sm.puri.Squeekboard.desktop'
 
 i18n.merge_file('desktop',
-    input: desktop_file + '.in',
+    input: configure_file(
+      input: desktop_file + '.in.in',
+      output: desktop_file + '.in',
+      configuration: desktopconf
+    ),
     output: desktop_file,
     po_dir: '../po',
     install: true,
-    install_dir: join_paths(datadir, 'applications'),
+    install_dir: desktopdir,
     type: 'desktop'
 )

data/sm.puri.Squeekboard.desktop.in.in

@@ -2,7 +2,7 @@
 Name=Squeekboard
 GenericName=Squeekboard Virtual Keyboard
 Comment=Virtual Keyboard
-Exec=squeekboard
+Exec=@bindir@/squeekboard
 Terminal=false
 Type=Application
 NoDisplay=true