Dockerfile: update `--from` options from `RUN` Dockerfile instructions when not first mount

[rarkins]

Discussed in #37280

^{Originally posted by aradkdj August 1, 2025}

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Support parsing version information from a RUN's --mount=from when a docker image does not appear as the first mount for the instruction.

Reproduction repo: https://github.com/aradkdj/renovate-37280-reproduction