Disallow empty parameter and argument names

[HertzDevil]

Resolves #11970.

def foo("" x); end   # Error: external parameter name cannot be empty
macro foo("" x); end # Error: external parameter name cannot be empty
foo("": 1)           # Error: named argument cannot have an empty name
Foo("": T)           # Error: named argument cannot have an empty name
fun foo(Int32); end  # Error: top-level fun parameter must have a name
{"": 1}              # Error: named tuple name cannot be empty

Annotations already produce an error before because their named arguments cannot use StringLiteral keys. The rest are breaking changes.