Support `pack build --platform`

[natalieparellano]

Fixes https://github.com/buildpacks/pack/issues/2154

Has a merge conflict with https://github.com/buildpacks/pack/pull/2086 - let's get that one in first and then update this one

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 76.00000% with 18 lines in your changes are missing coverage. Please review.

Project coverage is 70.18%. Comparing base (7306444) to head (89cb617).

Additional details and impacted files

[](https://app.codecov.io/gh/buildpacks/pack/pull/2162?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=buildpacks) ```diff @@ Coverage Diff @@ ## main #2162 +/- ## ========================================== + Coverage 70.15% 70.18% +0.03% ========================================== Files 253 253 Lines 18412 18449 +37 ========================================== + Hits 12916 12947 +31 - Misses 4650 4656 +6 Partials 846 846 ``` | [Flag](https://app.codecov.io/gh/buildpacks/pack/pull/2162/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=buildpacks) | Coverage Δ | | |---|---|---| | [os_linux](https://app.codecov.io/gh/buildpacks/pack/pull/2162/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=buildpacks) | `69.32% <74.67%> (+0.03%)` | :arrow_up: | | [os_macos](https://app.codecov.io/gh/buildpacks/pack/pull/2162/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=buildpacks) | `65.63% <60.00%> (+0.01%)` | :arrow_up: | | [os_windows](https://app.codecov.io/gh/buildpacks/pack/pull/2162/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=buildpacks) | `69.70% <76.00%> (+0.03%)` | :arrow_up: | | [unit](https://app.codecov.io/gh/buildpacks/pack/pull/2162/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=buildpacks) | `70.18% <76.00%> (+0.03%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=buildpacks#carryforward-flags-in-the-pull-request-comment) to find out more.

[jjbustamante]

This looks good to me, the only thing is adding back ImageOS: targetToUse.OS for testing because I didn't get any failure locally