Auto merge of #24473 - mmatyas:webgl_fns_buffer, r=jdm

Implement the basic WebGL2 buffer data operations

Adds support for the WebGL2 calls `bufferData`, `bufferSubData`, `copyBufferSubData` and `getBufferSubData`.

Reference: https://www.khronos.org/registry/webgl/specs/latest/2.0/#3.7.3

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This patch depends on https://github.com/servo/sparkle/pull/8. Some tests cause a crash for me at the moment, as they depend on other, not yet implemented buffer calls and transform feedback objects.

As for the code, there are a few parts I'm not sure about:

- To get the element byte size of a TypedArray I've wrote a simple `match`, as the relevant field is not published in `rust-mozjs`. Is that okay or there's some other way to get this already?
- The WebGL1 BufferData implementations were copied into the WebGL2 code as a workaround, due to the difference in the available buffer slots (ie. `self.bound_buffer`). An alternative could be is to pass this function and self as parameters to an internal buffer data implementation function, but personally I found that code to be quite ugly.

cc @jdm @zakorgy

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components/script/dom/webidls/WebGL2RenderingContext.webidl

@@ -299,18 +299,18 @@ interface mixin WebGL2RenderingContextBase
   void bufferData(GLenum target, GLsizeiptr size, GLenum usage);
   void bufferSubData(GLenum target, GLintptr dstByteOffset, /*[AllowShared]*/ BufferSource srcData);
   // WebGL2:
-  // void bufferData(GLenum target, [AllowShared] ArrayBufferView srcData, GLenum usage, GLuint srcOffset,
-  //                 optional GLuint length = 0);
-  // void bufferSubData(GLenum target, GLintptr dstByteOffset, [AllowShared] ArrayBufferView srcData,
-  //                    GLuint srcOffset, optional GLuint length = 0);
+  void bufferData(GLenum target, /*[AllowShared]*/ ArrayBufferView srcData, GLenum usage, GLuint srcOffset,
+                  optional GLuint length = 0);
+  void bufferSubData(GLenum target, GLintptr dstByteOffset, /*[AllowShared]*/ ArrayBufferView srcData,
+                     GLuint srcOffset, optional GLuint length = 0);
 
-  // void copyBufferSubData(GLenum readTarget, GLenum writeTarget, GLintptr readOffset,
-  //                        GLintptr writeOffset, GLsizeiptr size);
+  void copyBufferSubData(GLenum readTarget, GLenum writeTarget, GLintptr readOffset,
+                         GLintptr writeOffset, GLsizeiptr size);
   // MapBufferRange, in particular its read-only and write-only modes,
   // can not be exposed safely to JavaScript. GetBufferSubData
   // replaces it for the purpose of fetching data back from the GPU.
-  // void getBufferSubData(GLenum target, GLintptr srcByteOffset, [AllowShared] ArrayBufferView dstBuffer,
-  //                       optional GLuint dstOffset = 0, optional GLuint length = 0);
+  void getBufferSubData(GLenum target, GLintptr srcByteOffset, /*[AllowShared]*/ ArrayBufferView dstBuffer,
+                        optional GLuint dstOffset = 0, optional GLuint length = 0);
 
   /* Framebuffer objects */
   // void blitFramebuffer(GLint srcX0, GLint srcY0, GLint srcX1, GLint srcY1, GLint dstX0, GLint dstY0,