Rollup merge of #148723 - Zalathar:bootstrap-doctest, r=jieyouxu

bootstrap: Render doctest timing reports as text, not JSON

These doctest timing reports were added to libtest/rustdoc in rust-lang/rust#144909, but bootstrap's custom test-output renderer wasn't taught about them, so they were being printed as raw JSON instead.

Before:
```text
{ "type": "report", "total_time": 0.738403958, "compilation_time": 0.731513292 }
```

After:
```text
all doctests ran in 0.73s; merged doctests compilation took 0.72s
```

<details>
<summary><b>Detailed before/after in context</b></summary>

## Before

```text
$ x test rustc_mir_transform --doc
Building bootstrap
    Finished `dev` profile [unoptimized] target(s) in 0.03s
Testing stage1 {rustc_mir_transform} (aarch64-apple-darwin)
    Finished `release` profile [optimized + debuginfo] target(s) in 0.12s
   Doc-tests rustc_mir_transform

running 19 tests
iiiiiiiiiiii.......

test result: ok. 7 passed; 0 failed; 12 ignored; 0 measured; 0 filtered out; finished in 3.28ms

running 7 tests
iiiiiii

test result: ok. 0 passed; 0 failed; 7 ignored; 0 measured; 0 filtered out; finished in 403.67µs

{ "type": "report", "total_time": 0.738403958, "compilation_time": 0.731513292 }
	finished in 1.505 seconds
Build completed successfully in 0:00:01
```

## After

```text
$ x test rustc_mir_transform --doc
Building bootstrap
    Finished `dev` profile [unoptimized] target(s) in 0.03s
Testing stage1 {rustc_mir_transform} (aarch64-apple-darwin)
    Finished `release` profile [optimized + debuginfo] target(s) in 0.12s
   Doc-tests rustc_mir_transform

running 19 tests
iiiiiiiiiiii.......

test result: ok. 7 passed; 0 failed; 12 ignored; 0 measured; 0 filtered out; finished in 3.12ms

running 7 tests
iiiiiii

test result: ok. 0 passed; 0 failed; 7 ignored; 0 measured; 0 filtered out; finished in 395.67µs

all doctests ran in 0.73s; merged doctests compilation took 0.72s
	finished in 1.493 seconds
Build completed successfully in 0:00:01
```

</details>

Author: matthiaskrgr