Result#type and Result#prefix

[tompng]

To handle and override Symbol.all_symbols completion in IRB.
I'm thinking of using this from ruby/irb#1021

result = ReplTypeCompletor.analyze(':sym', binding:)
result.type #=> :symbol
result.prefix #=> "sym"

result = ReplTypeCompletor.analyze('[1, "2"].map(&:to_', binding:)
result.type #=> :call
result.prefix #=> "to_"
# Receiver type(Integer|String) of this :call is not exposed.

result = ReplTypeCompletor.analyze('def f(abc = 1); ab', binding:)
result.type #=> :lvar_or_method # abc(lvar) or abort(method)
result.prefix #=> "ab"
# Scope object (including self type, local variables) is not exposed.

Future plans

ReplTypeCompletor might drop returning Symbol.all_symbols because it has performance problem.

result = ReplTypeCompletor.analyze("puts :a", binding:)
result.type #=> :symbol
result.completion_candidates #=> [] (always empty array)

ReplTypeCompletor might add symbol hash key completion

hash = { foo: 1, bar: 2, baz: 3 }
result = ReplTypeCompletor.analyze("hash[:b", binding:)
result.type #=> :symbol or :symbol_hash_key(to distinguish from :symbol handled in IRB)
result.completion_candidates #=> ["ar", "az"]