feat: implement :read typed command

[idursun]

This is a naive attempt at partially implementing #3796

Adds a typed command :read with alias :r (following vim) that reads the contents of a file into the current buffer.

At this stage, I just would like to validate my approach and obviously would love to finish it off after implementing some integration tests.

I also appreciate any pointers and guidance around reading the file contents into the buffer more efficiently. I am loading the file into a String for now.

[pinpox]

Thanks for working on this! Would it be possible to integrate this with the file picker? Might be a separate PR though

[idursun]

@kirawi I have copied and used a trimmed down version of helix_view::document::from_reader that is using encoding_rs::Decoder::decode_to_string. I have also added an integration test that is only testing the happy path.

I appreciate it if you can have a look and let me know if you suggest any changes.

[the-mikedavis]

This duplicates a lot of code between this function and document::from_reader. Can you factor out the shared parts and share the code?

[idursun]

I agree. I was following @kirawi's advice on this: #3966 (comment)

I can try working something out at the expense of dragging this PR further, or that work can be the subject of another PR. I am easy either way. It's all up to the maintainers at this point.

[the-mikedavis]

This can use read_to_string from document now:

helix/helix-view/src/document.rs

Lines 474 to 477 in 636c91c

	pub fn read_to_string<R: std::io::Read + ?Sized>(
	reader: &mut R,
	encoding: Option<&'static Encoding>,
	) -> Result<(String, &'static Encoding, bool), Error> {

[sudormrfbin]

How about :read-file-into-buffer? :read isn't very descriptive of what it reads, what it does to the read file, etc. We can still have the aliases for :read and :r.

[idursun]

How about :read-file-into-buffer? :read isn't very descriptive of what it reads, what it does to the read file, etc. We can still have the aliases for :read and :r.

@sudormrfbin I have named it :read just to be aligned with vim's naming of the command.

[the-mikedavis]

Vi :read is more general - you can read the output of shell commands like :read !echo "foo"

We already have shell_insert_output for that case so I think we should limit this command to reading from files and have a name that reflects that

[pascalkuthe]

closing in favor of #10447