[llvm] [Dexter] Avoid incorrect state matching against frames below main (PR #206732)

[Stephen Tozer via llvm-commits]

SLTozer wrote:

> We currently check functions against a blocklist to determine whether they're "below main". I wonder why we don't discard all frames under the one called `main`? Seems a bit odd

There are some cases where "main" isn't actually called `main`, or other functions called `main` exist, and we want Dexter to behave itself in those cases.

> I'm not a huge fan of the idea of using `deemphasize` but I can't really put my finger on why. I think it's because it's subjective and possibly configurable in debuggers, thus feels prone to being wobbly in tests/ sensitive to environment.

I agree with the caution, since it's an optional field for "presentation" purposes which may feel wobbly. I decided on using it for a few reasons: firstly, although it's used for presentation purposes, it's not a "user-facing" string - it's interpreted by clients (such as vscode) for their display logic, and so it may be considered fairly reliable since it's used for cross-application communication, and therefore is likely to be stable and used fairly consistently. It's also part of the debugger display logic/UI, so it's not really out of Dexter's wheelhouse. It's not going to be universally reliable, but it's the only readily available option I see that adds "future-proofing", and we don't "lose" anything for adding it. Together this makes me feel the change is probably worth it, but if we're not sure then there may be other possible approaches.

https://github.com/llvm/llvm-project/pull/206732