Merge #1913 #1926 #1927 #1931 #1933

1913: feat: I/O safety for 'sys/inotify' r=asomers a=SteveLauC

#### What this PR does:

1. Changes the `fd` field of `struct Inotify` from `RawFd` to `OwnedFd`
2. Changes the interfaces of functions in the `impl Inotify {}`
   
    > The type of `self` changes from `Self` to `&mut Self`. 
    
    From:

   ```rust
   pub fn add_watch<P: ?Sized + NixPath>(
         self,
         path: &P,
         mask: AddWatchFlags,
   ) -> Result<WatchDescriptor> 

   pub fn rm_watch(self, wd: WatchDescriptor) -> Result<()>

   pub fn read_events(self) -> Result<Vec<InotifyEvent>>
   ```

   To:

   ```rust
   pub fn add_watch<P: ?Sized + NixPath>(
        &mut self,
        path: &P,
        mask: AddWatchFlags,
    ) -> Result<WatchDescriptor>

   pub fn rm_watch(&mut self, wd: WatchDescriptor) -> Result<()>

   pub fn read_events(&mut self) -> Result<Vec<InotifyEvent>>
   ```
  

   In the previous implementation, these functions can take `self` by value as `struct Inotify` [was `Copy`](https://docs.rs/nix/latest/nix/sys/inotify/struct.Inotify.html#impl-Copy-for-Inotify). With the changes in `1` applied, `struct Inotify` is no longer `Copy`, so we have to take `self` by reference.

-------

Blocks until the merge of #1863 as this PR needs `read(2)` to be I/O-safe.


1926: feat: I/O safety for 'sys/sendfile' r=asomers a=SteveLauC

#### What this PR does:
1. Adds I/O safety for module `sys/sendfile`.

1927: feat: I/O safety for 'sys/statvfs' r=asomers a=SteveLauC

#### What this PR does:
1. Adds I/O safety for module `sys/statvfs`.

1931: feat: I/O safety for 'sys/uid' & 'sched' r=asomers a=SteveLauC

#### What this PR does:
Adds I/O safety for modules:

1. `sys/uio`
2. `sched`

1933: feat: I/O safety for 'sys/timerfd' r=asomers a=SteveLauC

#### What this PR does:
1. Adds I/O safety  for module `sys/timerfd`.

Co-authored-by: Steve Lau <stevelauc@outlook.com>