Use folly::fileops qualified name

Summary:
This updates `open`, `close`, `read`, `write`, and `pipe` call sites to use
`folly::fileops` qualified name lookup.

This is the 2nd phase in a 3-phase change to remove folly's global definitions
of the posix functions that conflict with windows CRT.
The 1st phase created namespaces for folly's posix functions. The 2nd phase
updates callsites to use the qualified name of folly's  `open`, `close`,
`read`, `write`, and `pipe`  functions. The 3rd and final phase will remove
folly's globally defined posix functions and have windows CRT define them
again.

**What is the reason for this change?**
Folly's global definitions of posix functions on Windows causes `#include`
order issues if folly is not included first.

For example, when `gtest/gtest.h` is included before folly, gtest includes
`windows.h` and that declares `open`, `read`, and `chdir`, which creates
ambiguous references to folly's `open`, `read`, and `chdir`.

Another example is where posix functions go undeclared when
`folly/portability/windows.h` is included without other portability headers
(e.g., `folly/portability/unistd.h`). `folly/portability/windows.h` includes
`windows.h` in a way that only underscore versions of the posix functions are
available (e.g., `_open`, `_close`).

These issues create friction for windows development.

**Background: What is the purpose of `folly::portability::{fcntl,stdlib,sysstat,unistd}`?**
It is a portability layer to make posix functions available and behave
consistently across platforms. Some posix functions don't exist on windows
(e.g., `sysconf`). Some other posix functions, folly changes to adapt behavior
across platforms. For example, on windows folly defines `open`, `read`,
`write`, and `close` functions to work with sockets. Folly makes these
functions available in the global scope for convenience.

Reviewed By: Gownta

Differential Revision: D66191403

fbshipit-source-id: f3966b9b3af3bc5f498ef92dbdb202baa950b41d

folly/io/async/test/AsyncUDPSocketTest.cpp

@@ -378,7 +378,8 @@ class UDPNotifyClient : public UDPClient {
     SocketAddress addr;
     addr.setFromSockaddr(rawAddr, addrLen);
 
-    onDataAvailable(addr, size_t(read), false, OnDataAvailableParams());
+    onDataAvailable(
+        addr, size_t(folly::fileops::read), false, OnDataAvailableParams());
   }
 
   void onRecvMmsg(AsyncUDPSocket& sock) {

folly/test/FileUtilTest.cpp

@@ -267,7 +267,9 @@ TEST(FileUtilTest2, wrapv) {
 #ifndef _WIN32
   EXPECT_EQ(sum, wrapvFull(writev, tempFile.fd(), iov.data(), iov.size()));
 #else
-  EXPECT_EQ(sum, wrapvFull(write, tempFile.fd(), iov.data(), iov.size()));
+  EXPECT_EQ(
+      sum,
+      wrapvFull(folly::fileops::write, tempFile.fd(), iov.data(), iov.size()));
 #endif
 }
 

folly/test/IndexedMemPoolTest.cpp

@@ -79,7 +79,7 @@ TEST(IndexedMemPool, noStarvation) {
         EXPECT_LE(
             idx, poolSize + (pool.NumLocalLists - 1) * pool.LocalListLimit);
         pool[idx] = i;
-        EXPECT_EQ(write(fd[1], &idx, sizeof(idx)), sizeof(idx));
+        EXPECT_EQ(fileops::write(fd[1], &idx, sizeof(idx)), sizeof(idx));
         Sched::post(&readSem);
       }
     });