[Impeller] libImpeller: A C++ wrapper to the Impeller API. (#56682)

_`impeller.hpp` is to `impeller.h` what `vulkan.hpp` is to `vulkan.h`_

* A single header C++ 17 library that only depends on impeller.h and standard libc++ utilities.
* The C++ library proc. table is setup at runtime (via dlsym and related methods). Impeller users don't need to link against libimpeller.so as long as they can discover it at runtime.
* RAII wrappers for all opaque objects.
* Namespaces are configurable depending on target.
* Included in the distributed SDK next to impeller.h.

ci/licenses_golden/licenses_flutter

@@ -43505,7 +43505,9 @@ ORIGIN: ../../../flutter/impeller/toolkit/interop/image_filter.cc + ../../../flu
 ORIGIN: ../../../flutter/impeller/toolkit/interop/image_filter.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/toolkit/interop/impeller.cc + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/toolkit/interop/impeller.h + ../../../flutter/LICENSE
+ORIGIN: ../../../flutter/impeller/toolkit/interop/impeller.hpp + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/toolkit/interop/impeller_c.c + ../../../flutter/LICENSE
+ORIGIN: ../../../flutter/impeller/toolkit/interop/impeller_cc.cc + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/toolkit/interop/mask_filter.cc + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/toolkit/interop/mask_filter.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/toolkit/interop/object.cc + ../../../flutter/LICENSE
@@ -46406,7 +46408,9 @@ FILE: ../../../flutter/impeller/toolkit/interop/image_filter.cc
 FILE: ../../../flutter/impeller/toolkit/interop/image_filter.h
 FILE: ../../../flutter/impeller/toolkit/interop/impeller.cc
 FILE: ../../../flutter/impeller/toolkit/interop/impeller.h
+FILE: ../../../flutter/impeller/toolkit/interop/impeller.hpp
 FILE: ../../../flutter/impeller/toolkit/interop/impeller_c.c
+FILE: ../../../flutter/impeller/toolkit/interop/impeller_cc.cc
 FILE: ../../../flutter/impeller/toolkit/interop/mask_filter.cc
 FILE: ../../../flutter/impeller/toolkit/interop/mask_filter.h
 FILE: ../../../flutter/impeller/toolkit/interop/object.cc

impeller/toolkit/interop/BUILD.gn

@@ -31,7 +31,9 @@ impeller_component("interop") {
     "image_filter.h",
     "impeller.cc",
     "impeller.h",
+    "impeller.hpp",
     "impeller_c.c",
+    "impeller_cc.cc",
     "mask_filter.cc",
     "mask_filter.h",
     "object.cc",
@@ -119,13 +121,17 @@ zip_bundle("sdk") {
   deps = [ ":library" ]
 
   files = [
+    {
+      source = "README.md"
+      destination = "README.md"
+    },
     {
       source = "impeller.h"
       destination = "include/impeller.h"
     },
     {
-      source = "README.md"
-      destination = "README.md"
+      source = "impeller.hpp"
+      destination = "include/impeller.hpp"
     },
   ]