Add unstable go-to-stage option

[blyxyas]

Adds a go-to-stage flag, this flag makes the compiler exit after a certain stage. Currently it recognizes end (the default which is effectively a no-op), analysis for stopping after analysis and
nameres for stopping just after name resolution.

analysis is similar to --emit=metadata without link, and nameres will be used for the probe run in Cargo (See blyxyas/incr-systems#4)

Related to blyxyas/incr-systems#3 and rust-lang/goals#641
r? @jackh726

[rustbot]

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

[jackh726]

I don't think we should add a new flag here - I think we should be reusing --emit.

I think we likely need a couple things:

1. We need to ANALYSIS and ANALYSIS_FULL (or similar) output types to stop immediately after required and full analyses.
2. I don't think we should be doing something like "if emitting depinfo and nothing else" but rather "needs XYZ". Because we may want to do `--emit=depinfo,metadata"

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