Better error message for 16 byte alignment error

[IceSentry]

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
(Based on) Closes #3099
Closes #2832

Description
Previous error message was the generic downflags error message for BUFFER_BINDINGS_NOT_16_BYTE_ALIGNED that didn't highlight that if it was 16 bit aligned then this is supported. But it wasn't clear which shader group / bind was not aligned.

New error message:

In Device::create_render_pipeline
      note: label = `cuboids_pipeline`
    shader group 1 binding 1 must be 16 bytes aligned as device does not support DownlevelFlags `BUFFER_BINDINGS_NOT_16_BYTE_ALIGNED`

Also have switched the code around to check the flag once as if it's set then we can skip the check entirely.

Testing
I didn't test it myself, but the original author tested and I simply updated the message to address the comment on the PR

[IceSentry]

@cwfitzgerald btw, I replied to the code suggestion, but I know github notifications are a bit weird with resolved discussions so I'll ping you here.

[cwfitzgerald]

@IceSentry Good shout on the ping - I didn't see this. I just realized the requirement is that the size, not the alignment, is a multiple of 16. So my suggestion is actually slightly wrong. /s/alignment/size should take care of it. The requirement should be "a multiple of 16".

[cwfitzgerald]

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