build.ps1: make time summary hierarchical

[speednoisemovement]

Currently, summary timings are emitted at the end of operations. Each operation that needs to be timed has to instantiate a stopwatch when it begins, and writes the time provided by the stopwatch when it ends. This can cause nested operations to double-count elapsed time.

This change introduces two functional changes:

• Nested steps are now visually displayed as children of their parent step
• Only top-level steps contribute to the total time calculation

To allow for this, we need to track the operation from the beginning instead of just reporting at the end. Any block of code can now be timed by wrapping it in a Record-OperationTime call.

[compnerd]

I don't really understand the self-time vs total time. I get that an interior node will need a view of the summation of the sub-times, but why is the self-time useful there? That is, why not just have a singular value? What does the second timing give us?

[speednoisemovement]

What does the second timing give us?

Makes it obvious what we're not capturing elsewhere. For example, it's clear that Build-SDK is just a wrapper, but more than 50% of Build-ExperimentalSDK isn't otherwise timed. I did write this before I saw that the nesting only goes 1 level deep at the moment, so maybe it's overkill, but I do think it has value. Up to you!

[compnerd]

What does the second timing give us?

Makes it obvious what we're not capturing elsewhere. For example, it's clear that Build-SDK is just a wrapper, but more than 50% of Build-ExperimentalSDK isn't otherwise timed. I did write this before I saw that the nesting only goes 1 level deep at the moment, so maybe it's overkill, but I do think it has value. Up to you!

I think that we should try to keep this simple for now. The additional complexity can be added when needed.

[speednoisemovement]

What does the second timing give us?

Makes it obvious what we're not capturing elsewhere. For example, it's clear that Build-SDK is just a wrapper, but more than 50% of Build-ExperimentalSDK isn't otherwise timed. I did write this before I saw that the nesting only goes 1 level deep at the moment, so maybe it's overkill, but I do think it has value. Up to you!

I think that we should try to keep this simple for now. The additional complexity can be added when needed.

Done

[compnerd]

@swift-ci please smoke test