`parser`: improve using panic mode

[raklaptudirm]

Parse methods now return explicit errors. The errors are handled and the parser is synchronized by other methods. This reduces the number of cascaded errors reported by the parser.

[raklaptudirm]

This also reduces the number of cascaded errors, as previously even after an error the parser would keep trying to parse the wrong tokens, and would report a whole lot of errors that all stemmed from that single problem.

[raklaptudirm]

Still some work left on the parser but will open a separate pr for that.