optimize perfermance of fd_read/fd_write

[liutao-liu]

• Issue Poor performance of wasmtime file I/O maybe because tokio  #7973

Compared to native(C/C++), fd-read can only reach 20% of native. I will divide the performance hotspots into the following two categories:,

1. Wasi implementation of fd-read(approximately 30% of the hotspots), such as the cost of redundant memory copies, the cost of inserting and deleting HostInputStream into WasiView, and the cost of accessing guest memory(merged PR);
2. Wasm program call host function(approximately 40% of the hotspots): I am not very familiar with this mechanism yet, and currently I cannot understand the reasons behind the hotspots here;

This PR is mainly optimized for the first type of performance hotspot:

1. Avoid unnecessary copying;
2. Avoid inserting and deleting HostInputStream intoWasiView;

The perfermance hotspots of fd_write is the same fd_read:

wasmtime/crates/wasi/src/preview1.rs

Line 1682 in 86dcae4

let stream = self.append_via_stream(fd).map_err(|e| {

wasmtime/crates/wasi/src/preview1.rs

Line 244 in 86dcae4

Vec::from(chunk),

[alexcrichton]

Thanks for the PR!

I've left some notes below, but I'll additionally point out that this is specifically ignoring the blocking_mode now. Previously that was "respected" to a certain degree, but now it's being ignored. I believe that's ok because that's what the previous implementation in wasi-common did anyway as OSes tend to ignore nonblocking on files. That being said the current state of the code is a bit confusing where the blocking_mode is sometimes used and sometimes isn't.

I mostly wanted to point this out in case anyone runs into this in the future. I'll follow up with a PR after this one to clean this up. You don't have to clean it up here yourself @liutao-liu

[liutao-liu]

@alexcrichton Your review comments have been completed，this pr can be merged.