treewide: mark things static and const

Mark some structures, arrays static/const at various places.
In some cases this prevents unnecessary initialization
when a function is entered.

All in all, the text segments across all shared
libraries are reduced by about 2 KiB. However,
the total size increases by about 2 KiB as well.

src/modules/module-session-manager/client-session/session.c

@@ -275,7 +275,7 @@ int session_init(struct session *this,
 		struct pw_context *context,
 		struct pw_properties *properties)
 {
-	const char *keys[] = {
+	static const char * const keys[] = {
 		PW_KEY_FACTORY_ID,
 		PW_KEY_CLIENT_ID,
 		NULL