Allow trailing semicolon in list initializers

[TheBerkin]

List initializers should allow a trailing semicolon at the end of the element list without automatically creating an empty at the end of the list.

Proposal

The following rules should apply when parsing semicolons in a list initializer context:

An empty list initializer with no semicolons produces an empty list

This is the current behavior, but it is worth noting that this should remain the case.

() # empty list

A semicolon only guarantees a value to its left

Even if there is nothing before the semicolon, it should signal to the compiler that there should be an empty element.

(;) # same as (~)

A final value with a terminating semicolon acts the same one without it

If a list ends with a value and no trailing semicolon, it should compile to the same list as one with the semicolon.

# 2-item list without trailing semi
(a; b) 
# Same 2-item list with trailing semi
(a; b;)