Track follow-up improvements to Copilot agent setup steps

[ericstj]

This issue tracks follow-up work to improve the Copilot agent setup steps as discussed in PRs #115912, #115917.

@CarnaViire @ellismg

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Follow-up Items

• 1. Script for installing dependencies
• 2. Simplify restore step
• 3. Upload binlog from build step

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1. Script for installing dependencies

We can improve the developer documentation by making a single installation script be sufficient for setting up the repo.

This script can be linked by our public docs. It can represent the superset of all the steps we have in our codespaces configuration containers - so long as none are mutually exclusive or excessively costly. If any are omitted, then we should make sure to discuss them in the copilot instructions doc so that the agent knows how to manually run them when facing work of that type.

2. Simplify restore step

We should add a flag for build.sh subsets that means "everything". That should save us specifying the custom properties like /p:DotNetBuildTests=true and reacting to any potential subset additions.

The flag itself is tracked in #116016. This item tracks updating the restore step afterwards.

3. Upload binlog from build step

While the clr+libs build step is present in the setup, we could consider uploading the binlog from the build. That might be useful for diagnosing failures. https://docs.github.com/en/actions/writing-workflows/choosing-what-your-workflow-does/storing-and-sharing-data-from-a-workflow

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2025-05-26: UPD by @CarnaViire to include more items

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