Position.character is not clamped to line length

[krobelus]

LSP says about Position::character

If the character value is greater than the line length it defaults back
to the line length.

but from_proto::offset() doesnt' implement this

    let text_size = line_index.index.offset(line_col).ok_or_else(|| {
        format_err!("Invalid offset {line_col:?} (line index length: {:?})", line_index.index.len())
    })?;

I hit this because rust-analyzer crashes with the kakoune-lsp client because -- if there is no code action in the selection -- this client falls back to requesting code actions for the whole line by simply specifying Position::character=1e6.
I worked around the crash by sending the actual line length instead.

I'm not yet sure what we should do, following the protocol can help but the downside is that we're masking potential bugs

I haven't yet found a case where a client inherently needs this behavior, so it doesn't seem important.

[Veykril]

We can always clamp and just log an error when that happens instead of returning one