Complete keyword arguments

[tompng]

For obj.foo ba, ba can be an lvar, method or keyword that starts with ba.
We need to check two things, type of obj and scope at ba in a single analyze.
Completion candidates will be:

• keyword arguments names of obj.foo
• local variables in scope at ba
• methods of self in scope at ba

To do it, ReplTypeCompletion::TypeAnalyze::DigTargets is changed.

# This class is used to check if the node is analyze target, and to skip analyze for some node.
# For `def f;long_code;end; def g; 1.a`, `def f` is skipped, `1` is target_node.

# Only single target_node
DigTargets.new(parent_nodes_to_analyze, target_node){
  callback_when_analyzed_target_node
}
# ↓
# Multiple target nodes
dig_targets = DigTargets.new(parent_nodes_to_analyze)
dig_targets.on(node1){callback1}
dig_targets.on(node2){callback2}