Lower limit from API 21 to API 19 (#1701)

* Lower limit from API 21 to API 19

This was requested by an internal application. API 19 is when OpenGL
ES 3.0 support was added so there is no good reason for us to not
support this API level. The only trick is to avoid referring to the
glTexStorage2DMultisample symbol directly as it only exists in 3.1.

* Compile out code we never use

* Use reflection to handle shared EGL contexts pre-API 21.

* Remove comment

* More fixes required to run on API level 19

- dlym() fails for ashmem on API 19, so we only try on API 26+ instead.
- Older emulation for OpenGL ES 3.0 returns error states for valid API calls so we need to clear the GL error bit before we create the GL driver.
- Activity lifecycle changes since API 19 would cause animations to keep running and to reference destroyed objects.
- EGLContext.getNativeHandle() is new in API 21, we need to use reflection on API 19. The new code path uses the class loading trick to avoid a bytecode verification error on API 19.

* Filament now runs properly on API level 19

This commit adds a new api_level() API to libutils which can be used to
query the platform's API level. On Android it works as expected, other
platforms currently return 0.

libs/utils/src/ashmem.cpp

@@ -15,6 +15,7 @@
  */
 
 #include <utils/ashmem.h>
+#include <utils/api_level.h>
 
 #include <errno.h>
 #include <assert.h>
@@ -85,13 +86,15 @@ static int __ashmem_open() {
 }
 
 int ashmem_create_region(const char *name, size_t size) {
-
-    // dynamically check if we have "ASharedMemory_create" (should be the case since 26 (Oreo))
-    using TASharedMemory_create = int(*)(const char *name, size_t size);
-    TASharedMemory_create pfnASharedMemory_create =
-            (TASharedMemory_create)dlsym(RTLD_DEFAULT, "ASharedMemory_create");
-    if (pfnASharedMemory_create) {
-        return pfnASharedMemory_create(name, size);
+    // Fetch the API level to avoid dlsym() on API 19
+    if (api_level() >= 26) {
+        // dynamically check if we have "ASharedMemory_create" (should be the case since 26 (Oreo))
+        using TASharedMemory_create = int(*)(const char *name, size_t size);
+        TASharedMemory_create pfnASharedMemory_create =
+                (TASharedMemory_create)dlsym(RTLD_DEFAULT, "ASharedMemory_create");
+        if (pfnASharedMemory_create) {
+            return pfnASharedMemory_create(name, size);
+        }
     }
 
     int ret, save_errno;