Reland^2: Use "gfxstream" namespace

This reverts commit d37d7c8c0cdf6b84d453cb41e358094880a8f3b5.

Reland adds in aosp/2516595 which was only built on the "full"
target and removes namespace around window methods to satisfy
MacOS build.

Bug: b/271464937
Test: android build
Test: cmake build
Test: ATP MacOS build
Change-Id: Ida36ac16f9c3b98aedd744d21c9b27e9063a8eea
diff --git a/stream-servers/Hwc2.cpp b/stream-servers/Hwc2.cpp
index bf82ef1..b4629bd 100644
--- a/stream-servers/Hwc2.cpp
+++ b/stream-servers/Hwc2.cpp
@@ -14,6 +14,8 @@
 
 #include "Hwc2.h"
 
+namespace gfxstream {
+
 std::unique_ptr<FlatComposeRequest> ToFlatComposeRequest(
         const ComposeDevice* composeRequest) {
     auto flatComposeRequest = std::make_unique<FlatComposeRequest>();
@@ -35,3 +37,5 @@
     }
     return flatComposeRequest;
 }
+
+}  // namespace gfxstream
\ No newline at end of file