Rollup merge of rust-lang#129545 - notriddle:notriddle/toolbar-v2, r=GuillaumeGomez

rustdoc: redesign toolbar and disclosure widgets

Fixes rust-lang#77899
Fixes rust-lang#90310

## Preview

| before | after
| ------ | -----
| ![image](https://github.com/user-attachments/assets/ebeec185-3a72-481d-921e-a9a885f348d9) | ![image](https://github.com/user-attachments/assets/08735a65-99d1-4523-ab77-ddb164c0a5db)
| ![image](https://github.com/user-attachments/assets/ae8e0f24-49cb-445d-b9bd-cec9c57b94e7) | ![image](https://github.com/user-attachments/assets/ba484f94-b031-41fc-b8a8-6cd81be8fb6b)
| ![image](https://github.com/user-attachments/assets/8c2cc041-a138-4950-a12e-3d529c8a5339) | ![image](https://github.com/user-attachments/assets/e7f010bd-19e2-4711-85bf-3fd00c3e5647)
| ![image](https://github.com/user-attachments/assets/e2b63785-971c-489e-b069-eb85f6a30620) | ![image](https://github.com/user-attachments/assets/b65eea16-d6a3-4aa3-8a27-6ded74009010)
| ![image](https://github.com/user-attachments/assets/1c7b0901-a61a-4325-9d01-9d8b14b476aa) | ![image](https://github.com/user-attachments/assets/d4a485db-d9f1-4a62-94bc-a3d125ea6dc1)
| N/A | ![image](https://github.com/user-attachments/assets/7add0a2a-7fd7-483d-87ee-51ee45a2fe5d)
| ![image](https://github.com/user-attachments/assets/334f50bc-9f8d-42d9-a7df-95058f7cdfd5) | ![image](https://github.com/user-attachments/assets/451fcc22-b034-453c-ae4b-b948fd6bd779)
| ![image](https://github.com/user-attachments/assets/132f720c-802a-466d-bd55-c7a4750acdc3) | ![image](https://github.com/user-attachments/assets/177b7921-06c5-467d-87d3-9cdf88c4e50b)

https://notriddle.com/rustdoc-html-demo-12/toolbar-v2/std/index.html

## Description

This adds labels to the icons and moves them away from the search box.

These changes are made together, because they work together, but are based on several complaints:

* The [+/-] thing are a Reddit-ism. They don't look like buttons, but look like syntax <https://rust-lang.zulipchat.com/#narrow/stream/266220-t-rustdoc/topic/More.20visual.20difference.20for.20the.20.2B.2F-.20.20Icons>, <rust-lang#59851> (some of these are laundry lists with more suggestions, but they all mention [+/-] looking wrong)

* The settings, help, and summary buttons are also too hard to recognize <https://lwn.net/Articles/987070/>, <rust-lang#90310>, <rust-lang#14475 (comment)>, <https://internals.rust-lang.org/t/improve-rustdoc-design/12758> ("Not all functionality is self-explanatory, for example the [+] button in the top right corner, the theme picker or the settings button.")

The toggle-all and toggle-individual buttons both need done at once, since we want them to look like they go together. This changes them from both being [+/-] to both being arrows.

CC <rust-lang#113074 (comment)> and ``@jsha`` regarding the use of triangles for disclosure, which is what everyone wanted, but was pending a good toggle-all button. This PR adds a toggle-all button that should work.

Settings and Help are also migrated, so that the whole group can benefit from being described using actual words.

The breadcrumbs also get redesigned, so that they use less space, by shrinking the parent module path parts. This is done at the same time as the toolbar redesign because it's, effectively, moving space from the toolbar to the breadcrumbs.
This is aimed at avoiding any line wrapping at desktop sizes.

## Prior art

This style of toolbar, with explicit labels on the buttons, used to be more popular. It's not very common in web browsers nowadays, and for truly universal icons like ⬅️ I can understand why, but words are great when icons fail.

![image](https://github.com/user-attachments/assets/9a4a0498-232d-4d60-87b9-f601f4515254)

Author: compiler-errors

std/src/lib.rs

@@ -32,13 +32,17 @@
 //!
 //! Once you are familiar with the contents of the standard library you may
 //! begin to find the verbosity of the prose distracting. At this stage in your
-//! development you may want to press the `[-]` button near the top of the
-//! page to collapse it into a more skimmable view.
-//!
-//! While you are looking at that `[-]` button also notice the `source`
-//! link. Rust's API documentation comes with the source code and you are
-//! encouraged to read it. The standard library source is generally high
-//! quality and a peek behind the curtains is often enlightening.
+//! development you may want to press the <code>
+//! <svg style="width:0.75rem;height:0.75rem" viewBox="0 0 12 12"
+//! stroke="currentColor" fill="none">
+//! <path d="M2,2l4,4l4,-4M2,6l4,4l4,-4"/></svg> Summary</code> button near the
+//! top of the page to collapse it into a more skimmable view.
+//!
+//! While you are looking at the top of the page, also notice the
+//! <code>source</code> link. Rust's API documentation comes with the source
+//! code and you are encouraged to read it. The standard library source is
+//! generally high quality and a peek behind the curtains is
+//! often enlightening.
 //!
 //! # What is in the standard library documentation?
 //!