Implement file metadata, read, and write APIs.

This also improves how HANDLEs are, well, handled a bit. STDIN/ERR/OUT are now proper pseudo-handles. The invalid handle is added and encode/decodes to exactly 0xFFFFFFFF correctly.

Unix shims require changes to hoist FdTable up, so that Windows can share most of its implementation.

Author: CraftSpider

Diff for: src/shims/files.rs

@@ -87,6 +87,7 @@ const WINDOWS_IO_ERROR_TABLE: &[(&str, std::io::ErrorKind)] = {
         ("ERROR_ACCESS_DENIED", PermissionDenied),
         ("ERROR_FILE_NOT_FOUND", NotFound),
         ("ERROR_INVALID_PARAMETER", InvalidInput),
+        ("ERROR_FILE_EXISTS", AlreadyExists),
     ]
 };
 

Diff for: src/shims/io_error.rs

@@ -8,6 +8,7 @@ mod unix;
 mod wasi;
 mod windows;
 mod x86;
+mod files;
 
 pub mod env;
 pub mod extern_static;
@@ -18,7 +19,8 @@ pub mod panic;
 pub mod time;
 pub mod tls;
 
-pub use self::unix::{DirTable, EpollInterestTable, FdTable};
+pub use self::unix::{DirTable, EpollInterestTable};
+pub use self::files::FdTable;
 
 /// What needs to be done after emulating an item (a shim or an intrinsic) is done.
 pub enum EmulateItemResult {