context: scale max_quantum and add quantum_limit

Also scale the max_quantum with the selected rate. Add a new
quantum_limit property that is the upper limit of the quantum regardless
of the sample rate, this is usually the allocated buffer size.

See #1931

src/pipewire/private.h

@@ -61,6 +61,7 @@ struct settings {
 	uint32_t clock_quantum;			/* default quantum */
 	uint32_t clock_min_quantum;		/* min quantum */
 	uint32_t clock_max_quantum;		/* max quantum */
+	uint32_t clock_quantum_limit;		/* quantum limit */
 	struct spa_rectangle video_size;
 	struct spa_fraction video_rate;
 	uint32_t link_max_buffers;