Auto merge of #51803 - lucasem:rustdoc-code-hash-escape, r=GuillaumeGomez

rustdoc codeblock hash escape

So that docstring text such as the following (in a code block) can be created ergonomically:

```rust
let s = "
    foo
    # bar
    baz
";
```

Such code in a docstring hide the <code>&nbsp;&nbsp;&nbsp;&nbsp;# bar</code> line.

Previously, using two consecutive hashes <code>&nbsp;&nbsp;&nbsp;&nbsp;## bar</code> would turn the line into _shown_ `# bar`, losing the leading whitespace. A line of code like <code>&nbsp;&nbsp;&nbsp;&nbsp;# bar</code> (such as in the example above) **could not be represented** in the docstring text.

This commit makes the two consecutive hashes not also trim the leading whitespace — the two hashes simply **escape** into a single hash and do not hide the line, leaving the rest of that line unaffected. The new docstring text to achieve the above code block is:

```rust
/// ```
/// let s = "
///     foo
///     ## bar
///     baz
/// ";
/// ```
```

0 files changed, 0 insertions, 0 deletions