cmd/compile/internal/syntax: factor out list parsing
Instead of repeating the same list parsing pattern for parenthesized
of braced comma or semicolon-separated lists, introduce a single list
parsing function that can be parametrized and which takes a closure
to parse list elements.
This ensures the same error handling and recovery logic is used across
all lists and simplifies the code.
No semantic change.
Change-Id: Ia738d354d6c2e0c3d84a5f1c7269a6eb95685edc
Reviewed-on: https://go-review.googlesource.com/70492 Reviewed-by: Matthew Dempsky <mdempsky@google.com>