Change the last 3 files in kebab-case to snake_case

[run1t]

There is only 3 files left in kebab-case in the src folder, this pull request put those in snake_case like the rest of the files for consistency.

[markholmes]

Might be irrelevant (and I'm new to this project so I don't have a lot of context), but there are also the compile/render-dom and compile/render-ssr folders and didn't see any documentation on it.

[run1t]

yes you're right having folder names in kebab-case and file names in snake_case seems inconsitent to me. All names should follow the same cases.

But it's seems weird to use snake_case on folder name. It's not difficult to change thought, so maybe I'll try to change them to snake_case to see how it's look.

[Rich-Harris]

Going to close this in favour of #3094 because of merge conflicts — thanks