AutoExposure doesn't seem to work on web about bevy

[rparrett]

The failure seems to be in the 2d_shapes example... so potentially

• doesn't work on webgl2 (iirc this is a known limitation)
• is enabled by default even in webgl2 builds in that PR
• is enabled by default even for 2d cameras in that PR

wgpu error: Validation Error

Caused by:
    In Device::create_bind_group_layout
      note: label = `compute histogram bind group`
    Too many bindings of type DynamicStorageBuffers in Whole pipeline, limit is 0, count was 1. Check the limit `max_dynamic_storage_buffers_per_pipeline_layout` passed to `Adapter::request_device`