textDocument/formatting requests removes whitespaces lines

[alexheretic]

RLS formatting can remove some whitespace lines that cargo fmt does not.
Downstream: rust-lang/atom-ide-rust#146

Example

fn main() {
    let foo = 123;
    
    let bar = 234;
}

Before

Note: line 3 is 4 spaces.

After textDocument/formatting

RLS responds with:

[{"range":{"start":{"line":6,"character":0},"end":{"line":7,"character":0}},"newText":""}]

So the blank line is removed.

Expected behaviour: cargo fmt

cargo fmt trims the line without removing.