On unclosed `impl`, documentSymbol symbol name can span many lines

[krobelus]

I'm not sure if there's anything to do here but I found this interesting.

No minimal reproducer but it should be reproducible on any impl block like below.
Cursor is at |

impl Foo<|
impl Bar<Baz> for Baz {
    ...
}

Now textDocument/documentSymbol will report a symbol with a name that starts at
impl Foo and spans across the impl Bar block and even further (in my case,
another impl block and a global function). I think it would be more intuitive to not report a symbol, or give it the name impl Foo<.

As workaround I'll truncate symbol names after the first line for now

[Veykril]

Probably parser recovery just eating everything as an error node when encountering the impl keyword in the generic param list