Audio buffer view improvements

[messmerd]

After some experience using the new audio buffer views in #7459 and #7858, it became clear that there was some useful quality-of-life functionality still missing (especially in InterleavedBufferView).

This PR adds that extra functionality we found useful.

EDIT: It looks like some of the commit messages got messed up due to me using backticks from the command-line.

[sakertooth]

Just a quick review, mostly looks fine.

[sakertooth]

I was making an AudioLayoutConverter class for #7568. I ended up needing to implement 4 separate functions, with the only differences being whether it's planar, interleaved, or both planar or both interleaved. I was considering a AudioBufferView that is essentially abstracting both planar and interleaved formats, but I was concerned about the performance and if there is a better way.

[sakertooth]

I could template it I guess.

[messmerd]

@sakertooth How about this:

template<class T, SampleType U, proc_ch_t channels = DynamicChannelCount>
concept AnyBufferView = std::convertible_to<T, InterleavedBufferView<U, channels>>
    || std::convertible_to<T, PlanarBufferView<U, channels>>;

You could use it like this:

void foo(AnyBufferView<const float, 2> auto in, AnyBufferView<float, 2> auto out)
{
}

Or without using the abbreviated function template syntax:

template<AnyBufferView<const float, 2> In, AnyBufferView<float, 2> Out>
void foo(In in, Out out)
{
}

EDIT: For ease of use, InterleavedBufferView and PlanarBufferView might need to define a static constexpr value or method that indicates whether it is interleaved or not:

void foo(AnyBufferView<const float, 2> auto buffer)
{
    if constexpr (decltype(buffer)::interleaved())
    {
        // `buffer` is interleaved
    }
    else
    {
        // `buffer` is planar
    }
}

[sakertooth]

Haven't done any testing but the changes look good as of right now. You can merge if you feel its ready.

[sakertooth]

Thought about it some more, and I think I prefer AudioBufferView rather than AnyBufferView. The audio part still gives context that this is a view over an audio buffer.

[sakertooth]

Apologies, I should've tested this PR in something like #7858 before approving. I think there was a slight error here: Shouldn't it be possible to convert from InterleavedBufferView<float, 2> to InterleavedBufferView<const float>?