media_error: Add MediaStatus::from_status_if_negative() helper

[MarijnS95]

CC @paxbun

Covers a prevalent unwrap_err() pattern for negative status codes, where we want to use any non-negative status code as a useful value and otherwise assert that from_status() turns the raw value into an appropriate error code (never into Ok(()), which should be unreachable in the current implementation).

Note that we cannot rely on from_status() returning Ok(()) or Err(_) and translate the Ok(()) back to the original value, as it handles (as of writing) two positive error codes which only relate to a specific AMediaCodec API, and any unrecognized codes including >0 are treated as UnknownStatus.

The function consumes Into<isize> instead of i32/c_int or ffi::media_status_t to support passing through numbers from various APIs that return 64-bit numbers (e.g. MediaCodec). The value only needs to be truncated (with a panic on try_into()) when it is lower than zero and needs to be converted to ffi::media_status_t.

[rib]

Urgh, kinda horrible that media_status_t has some non-negative status codes if some apis are designed to convey errors via negative values or else useful values :/

This utility API looks good to me though.

[MarijnS95]

Yeah doesn't have too much to do with this extra util function, but yes it is totally unusable because these error codes are supposedly only returned by API/functions that also have other non-zero positive return values 😩

Come to think of it, I don't think the current code handles those positive codes at all.