rust-analyzer should not emit macro-errors when macro input contains an unclosed delimiter

[dhardy]

Something which frequently frustrates me with rust-analyzer:

1. I am editing a Kas widget (to reproduce: clone Kas, pick any widget (but especially a large one; maybe try Spinner), and start typing a new fn with an unclosed brace: {)
2. RA correctly emits

   [rust-analyzer] (syntax-error) Syntax Error: expected R_CURLY

3. RA also emits

   [rust-analyzer] (macro-error) unexpected end of input, expected one of: enum, struct, type, union

The latter error causes the whole impl_scope to be marked as erroneous by the editor, making it harder to focus on the actual error.

Meanwhile, cargo check will only report

error: this file contains an unclosed delimiter
[details omitted]

Macros cannot be evaluated on input that won't even tokenize.

[ChayimFriedman2]

rustc can stop compilation when there is an error. rust-analyzer doesn't have this luxury: we must, always, do everything, even with erroneous code. The error marking the whole macro red is bad, though - it'll be better if it would only mark the expected place red, although I'm unsure how viable this is.