Add read_to_end for AnonPipe

Add `read_to_end` method for `sys::{target}::pipe::AnonPipe`. This allows
having a more optimized version of `read_to_end` for ChildStdout.

Signed-off-by: Ayush Singh <ayushsingh1325@gmail.com>

library/std/src/process.rs

@@ -362,6 +362,10 @@ impl Read for ChildStdout {
     fn is_read_vectored(&self) -> bool {
         self.inner.is_read_vectored()
     }
+
+    fn read_to_end(&mut self, buf: &mut Vec<u8>) -> io::Result<usize> {
+        self.inner.read_to_end(buf)
+    }
 }
 
 impl AsInner<AnonPipe> for ChildStdout {

library/std/src/sys/unix/pipe.rs

@@ -58,6 +58,10 @@ impl AnonPipe {
         self.0.is_read_vectored()
     }
 
+    pub fn read_to_end(&self, buf: &mut Vec<u8>) -> io::Result<usize> {
+        self.0.read_to_end(buf)
+    }
+
     pub fn write(&self, buf: &[u8]) -> io::Result<usize> {
         self.0.write(buf)
     }

library/std/src/sys/unsupported/pipe.rs

@@ -15,6 +15,10 @@ impl AnonPipe {
         self.0
     }
 
+    pub fn read_to_end(&self, buf: &mut Vec<u8>) -> io::Result<usize> {
+        self.0
+    }
+
     pub fn write(&self, _buf: &[u8]) -> io::Result<usize> {
         self.0
     }

library/std/src/sys/windows/pipe.rs

@@ -1,7 +1,7 @@
 use crate::os::windows::prelude::*;
 
 use crate::ffi::OsStr;
-use crate::io::{self, IoSlice, IoSliceMut};
+use crate::io::{self, IoSlice, IoSliceMut, Read};
 use crate::mem;
 use crate::path::Path;
 use crate::ptr;
@@ -261,6 +261,10 @@ impl AnonPipe {
         self.inner.is_read_vectored()
     }
 
+    pub fn read_to_end(&self, buf: &mut Vec<u8>) -> io::Result<usize> {
+        self.handle().read_to_end(buf)
+    }
+
     pub fn write(&self, buf: &[u8]) -> io::Result<usize> {
         unsafe {
             let len = crate::cmp::min(buf.len(), c::DWORD::MAX as usize) as c::DWORD;