Build failed with buildkit experimental features

[shizhMSFT]

Is this a BUG REPORT or FEATURE REQUEST?:
FEATURE REQUEST

What happened?:
az acr task run failed since the syntax of FROM with --platform in the Dockerfile (see example) is not supported.

What did you expect to happen?:
Build normally.

How do you reproduce it (as minimally and precisely as possible)?:

Environment:

Anything else we need to know?: