meson: add a plugin summary

This summary displays a list of plugins which
have been enabled.

Part-of: <!65>

meson.build

@@ -286,3 +286,18 @@ endif
 configure_file(output : 'config.h', configuration : cdata)
 
 run_command(python3, '-c', 'import shutil; shutil.copy("hooks/pre-commit.hook", ".git/hooks/pre-commit")')
+
+if meson.version().version_compare('>= 0.54')
+  plugin_names = []
+  foreach plugin: plugins
+    # FIXME: Use str.subtring() when we can depend on Meson 0.56
+    split = plugin.name().split('gst')
+    if split.length() == 2
+      plugin_names += [split[1]]
+    else
+      warning('Need substring API in meson >= 0.56 to properly parse plugin name: ' + plugin.name())
+      plugin_names += [plugin.name()]
+    endif
+  endforeach
+  summary({'Plugins':plugin_names}, list_sep: ', ')
+endif