Reject older versions of PipeWire than built against

Newer versions of PipeWire may add things to public structures. For example,
pw_buffer::requested added in 0.3.49. Building against 0.3.49 or newer, but
then running with 0.3.48 could result in invalid accesses since the returned
pw_buffer objects are shorter than the definition says to expect, creating
undefined behavior. Even if explicit access to the additional fields is
protected by a runtime check, the language allows the compiler to assume a
pointer to a pw_buffer object contains a complete pw_buffer, allowing the
optimizer to access the field earlier than the check (with the check only
controlling if the value gets used).

Another example is pw_time, which had a few fields added in 0.3.50 along with a
function, pw_stream_get_time_n, that provides the size of the pw_time struct
the application is using (so the library knows what version of the struct it
has to fill in). If a later version adds a new field, running it with an older
version will either fail (due to the library getting a size larger than it
knows about) or silently leave the newer fields as garbage.

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