Extract an arguments struct for `Builder::then_else_break`

Most of this method's arguments are usually or always forwarded as-is to recursive invocations.

Wrapping them in a dedicated struct allows us to document each struct field, and lets us use struct-update syntax to indicate which arguments are being modified when making a recursive call.

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While trying to understand the lowering of `if` expressions, I found it difficult to keep track of the half-dozen arguments passed through to every call to `then_else_break`. I tried switching over to an arguments struct, and I found that it really helps to make sense of what each argument does, and how each call is modifying the arguments.

I have some further ideas for how to streamline these recursive calls, but I've kept those out of this PR so that it's a pure refactoring with no behavioural changes.

…llaumeGomez

Rollup of 9 pull requests

Successful merges:

 - rust-lang#120976 (constify a couple thread_local statics)
 - rust-lang#121576 (Convert the rest of the visitors to use `VisitorResult`)
 - rust-lang#121826 (Use root obligation on E0277 for some cases)
 - rust-lang#121928 (Extract an arguments struct for `Builder::then_else_break`)
 - rust-lang#121958 (Fix redundant import errors for preload extern crate)
 - rust-lang#121959 (Removing absolute path in proc-macro)
 - rust-lang#121968 (Don't run test_get_os_named_thread on win7)
 - rust-lang#121977 (Doc: Fix incorrect reference to integer in Atomic{Ptr,Bool}::as_ptr.)
 - rust-lang#121978 (Fix duplicated path in the "not found dylib" error)

r? `@ghost`
`@rustbot` modify labels: rollup

Extract an arguments struct for `Builder::then_else_break`

Most of this method's arguments are usually or always forwarded as-is to recursive invocations.

Wrapping them in a dedicated struct allows us to document each struct field, and lets us use struct-update syntax to indicate which arguments are being modified when making a recursive call.

---

While trying to understand the lowering of `if` expressions, I found it difficult to keep track of the half-dozen arguments passed through to every call to `then_else_break`. I tried switching over to an arguments struct, and I found that it really helps to make sense of what each argument does, and how each call is modifying the arguments.

I have some further ideas for how to streamline these recursive calls, but I've kept those out of this PR so that it's a pure refactoring with no behavioural changes.