Hi. Currently, Zed uses incorrect indentation for singleton methods:

```ruby
def self.build
| # <= cursor position after hitting Enter
end
```

Handling the `singleton_method` token indentation
changes this behavior to the following:

```ruby
def self.build
  | # <= cursor position after hitting Enter
end
```

## Before


https://github.com/zed-industries/zed/assets/1894248/40fc2b37-692f-469f-9cbe-05cbb1ab4c3c

## After



https://github.com/zed-industries/zed/assets/1894248/d9ba8d27-fd17-4c74-b22c-a4de124739a3



Release Notes:

- N/A