Parser: recover on unfinished identifiers

[auduchinok]

Adds lexer recovery for unfinished escaped identifiers, and adds parser recovery for such identifiers.
Also aligns lexer rules for these idents with lexers we have in Rider.

`    // invalid empty identifier, token length is 1
``   // unfinished identifier containing all symbols until the line end
```  // unfinished identifier containing all symbols until the line end
```` // invalid empty identifier, token length is 4

type T() =
    [<Test>]
    member _.````() = () // invalid empty identifier