rustdoc: Break bounds if they are too long

[GuillaumeGomez]

Fixes #107283.

I'm not super happy with this fix, however, to do better, either we have to make the display implementation take into account a max length and therefore change how we render things completely or we could also parse HTML.

In this PR, I decided to take another approach: if there are more than 4 bounds on an item, these bounds are split each on their own line. We could also decide to group them by 2 or more.

I uploaded an example of it here.

r? @notriddle

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configure: rust.debug-assertions := True
configure: rust.overflow-checks := True
configure: llvm.assertions      := True
configure: dist.missing-tools   := True
configure: build.configure-args := ['--enable-sccache', '--disable-manage-submodu ...
configure: writing `config.toml` in current directory
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configure: run `python /checkout/x.py --help`
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tidy check
tidy: Skipping binary file check, read-only filesystem
Found 504 error codes
Highest error code: `E0792`
tidy error: /checkout/tests/rustdoc/lot-of-bounds.rs:8: line longer than 100 chars
some tidy checks failed
Build completed unsuccessfully in 0:00:22

[fmease]

The relevant issue states that rustdoc version 1.66.1 used to properly break the bounds into several lines meaning that the current state of affairs is a regression. Do you know which PR might have caused this regression? Why can't we do as before? Just curious.

[tspiteri]

In version 1.66.1 the bounds were not broken automatically; in the example that I showed they were broken up in the source. So the change in 1.67.0 is that it changes for example this source code

pub trait T
where
    Self: A + B + C,
    Self: D + E + F,
{

into

pub trait T
where
    Self: A + B + C + D + E + F,
{

[GuillaumeGomez]

@fmease: This is the PR which broke it: #105183. So this regression is a side-effect.

[bors]

☔ The latest upstream changes (presumably #107650) made this pull request unmergeable. Please resolve the merge conflicts.

[anden3]

Hello @GuillaumeGomez! I just want to ping you as part of the triage procedure as this PR has merge conflicts and CI failures :)

[GuillaumeGomez]

Doesn't seem like the right approach.