Update docs for EMSCRIPTEN_WEBGL_CONTEXT_HANDLE. NFC

This was changed in emscripten-core#20678

Fixes: emscripten-core#20993

Author: sbc100

site/source/docs/api_reference/html5.h.rst

@@ -1926,7 +1926,7 @@ Defines
 
 .. c:type:: EMSCRIPTEN_WEBGL_CONTEXT_HANDLE
 
-  Represents a handle to an Emscripten WebGL context object. The value 0 denotes an invalid/no context (this is a typedef to an ``int``).
+  Represents a handle to an Emscripten WebGL context object. The value 0 denotes an invalid/no context (this is a typedef to an ``intptr_t``).
 
 
 Struct