drm_hwcomposer: Rework autofd

Motivation:

Current implementation of UniqueFd can be used in a different ways,
making analytical tracking of FD lifecycle much harder than it may be.
Keep this part clean is very important, since any wrong code may open
a hard-to-detect runtime bugs and fd leaks, which may accidentally slip
into the production.

Implementation:

1. Combine UniqueFd anf OutputFd into single class.
2. Reduce the API to be minimal and sufficient.
3. Document the API and use cases.
4. Move to utils/UniqueFd.h.
5. dup(fd) was replaced with fcntl(fd, F_DUPFD_CLOEXEC)) to
   address clang-tidy findings. Find more information at [1]

[1]: https://clang.llvm.org/extra/clang-tidy/checks/android-cloexec-dup.html

Signed-off-by: Roman Stratiienko <r.stratiienko@gmail.com>
diff --git a/drm/DrmDevice.cpp b/drm/DrmDevice.cpp
index d9198d4..abc8edc 100644
--- a/drm/DrmDevice.cpp
+++ b/drm/DrmDevice.cpp
@@ -122,7 +122,7 @@
 
 std::tuple<int, int> DrmDevice::Init(const char *path, int num_displays) {
   /* TODO: Use drmOpenControl here instead */
-  fd_.Set(open(path, O_RDWR | O_CLOEXEC));
+  fd_ = UniqueFd(open(path, O_RDWR | O_CLOEXEC));
   if (fd() < 0) {
     ALOGE("Failed to open dri %s: %s", path, strerror(errno));
     return std::make_tuple(-ENODEV, 0);
@@ -585,9 +585,9 @@
 }
 
 std::string DrmDevice::GetName() const {
-  auto *ver = drmGetVersion(fd_.get());
+  auto *ver = drmGetVersion(fd());
   if (!ver) {
-    ALOGW("Failed to get drm version for fd=%d", fd_.get());
+    ALOGW("Failed to get drm version for fd=%d", fd());
     return "generic";
   }