Journal replay: Ensure full reuse of file descriptor space

[theduke]

#4990 fixed a bug in the journal replay logic which led to invalidly re-used file descriptors.

That PR implements a "quick fix" though, and breaks the convention of always re-using the lowest available FD number.
It instead just sets the next available FD to the highest used FD value.

To conform to the regular behaviour of "always use the lowest available FD number", the logic needs to be augmented to properly restore the FD number free list (freed_fds, located here:

wasmer/lib/wasix/src/fs/mod.rs

Line 511 in 9a7b33a

pub freed_fds: Arc<RwLock<BinaryHeap<Reverse<WasiFd>>>>,

).