Rollup merge of #119756 - notriddle:notriddle/reuse-map, r=GuillaumeGomez

rustdoc-search: reuse individual types in function signatures

Because `search.js` never mutates the function signature after loading it,
they can be safely and easily reused across functions.

This change doesn't change the format of the search index.
It only changes `search.js`.

Profiler output: https://notriddle.com/rustdoc-html-demo-9/fn-signature-opti2/index.html

<table><tr><th>benchmark<th>before<th>after

<tr><th>arti<td>

```
user: 002.228 s
sys:  000.315 s
wall: 001.663 s
child_RSS_high:     315668 KiB
group_mem_high:     285948 KiB
```

<td>

```
user: 001.805 s
sys:  000.231 s
wall: 001.398 s
child_RSS_high:     235864 KiB
group_mem_high:     203056 KiB
```

<tr><th>cortex-m<td>

```
user: 000.143 s
sys:  000.035 s
wall: 000.140 s
child_RSS_high:      59168 KiB
group_mem_high:      23000 KiB
```

<td>

```
user: 000.138 s
sys:  000.031 s
wall: 000.133 s
child_RSS_high:      58944 KiB
group_mem_high:      22220 KiB
```

<tr><th>sqlx<td>

```
user: 000.792 s
sys:  000.115 s
wall: 000.536 s
child_RSS_high:     156716 KiB
group_mem_high:     122948 KiB
```

<td>

```
user: 000.824 s
sys:  000.084 s
wall: 000.535 s
child_RSS_high:     136668 KiB
group_mem_high:     101792 KiB
```

<tr><th>stm32f4<td>

```
user: 006.665 s
sys:  003.533 s
wall: 008.624 s
child_RSS_high:    1037660 KiB
group_mem_high:    1022516 KiB
```

<td>

```
user: 005.997 s
sys:  003.185 s
wall: 007.987 s
child_RSS_high:     832068 KiB
group_mem_high:     810908 KiB
```

<tr><th>stm32f4xx-hal<td>

```
user: 000.317 s
sys:  000.051 s
wall: 000.203 s
child_RSS_high:      77060 KiB
group_mem_high:      41776 KiB
```

<td>

```
user: 000.287 s
sys:  000.046 s
wall: 000.180 s
child_RSS_high:      75216 KiB
group_mem_high:      39200 KiB
```

<tr><th>ripgrep<td>

```
user: 000.463 s
sys:  000.063 s
wall: 000.295 s
child_RSS_high:     101288 KiB
group_mem_high:      66364 KiB
```

<td>

```
user: 000.472 s
sys:  000.036 s
wall: 000.247 s
child_RSS_high:      82708 KiB
group_mem_high:      47056 KiB
```

</tr></table>

Author: GuillaumeGomez