[v0.15] WebGl workaround for drawing single instance

[Wumpf]

Checklist

• Run cargo clippy.
• Run RUSTFLAGS=--cfg=web_sys_unstable_apis cargo clippy --target wasm32-unknown-unknown if applicable.
• Add change to CHANGELOG.md. See simple instructions inside file.

Connections
#3578

Description
Whenever there is any instance attribute, we need to need use an instanced draw call on ANGLE. Otherwise, the following error will be (potentially spuriously) generated and may render incorrectly:

[.WebGL-0000554C38753500] GL_INVALID_OPERATION: Error: 0x00000502, in ..\..\third_party\angle\src\libANGLE\renderer\d3d\VertexDataManager.cpp, reserveSpaceForAttrib:520. Internal error: 0x00000502: Vertex buffer is not big enough for the draw call.

Testing
Tested on https://github.com/rerun-io/rerun