Implement translation for PM_LAMBDA_NODE

[amomchilov]

Special considerations:

• Ensure this works with numbered parameters, by un-commenting this test introduced in Implement Prism -> Sorbet translation for numbered block parameters (_1, _2, ...) #283
  

  sorbet/test/prism_regression/numbered_params.rb

  Lines 5 to 6 in 5234ff7

  	# TODO: uncomment once we support lambdas https://github.com/Shopify/sorbet/issues/125
  	# -> { _1 + _2 }

[st0012]

Sorbet parser's way of parsing lambda is pretty surprising to me.

Given

-> { 123 }

Prism gives:

@ ProgramNode (location: (1,0)-(1,10))
├── flags: ∅
├── locals: []
└── statements:
    @ StatementsNode (location: (1,0)-(1,10))
    ├── flags: ∅
    └── body: (length: 1)
        └── @ LambdaNode (location: (1,0)-(1,10))
            ├── flags: newline
            ├── locals: []
            ├── operator_loc: (1,0)-(1,2) = "->"
            ├── opening_loc: (1,3)-(1,4) = "{"
            ├── closing_loc: (1,9)-(1,10) = "}"
            ├── parameters: ∅
            └── body:
                @ StatementsNode (location: (1,5)-(1,8))
                ├── flags: ∅
                └── body: (length: 1)
                    └── @ IntegerNode (location: (1,5)-(1,8))
                        ├── flags: newline, static_literal, decimal
                        └── value: 123

But Sorbet's legacy parser give:

Block {
  send = Send {
    receiver = Const {
      scope = NULL
      name = <C <U Kernel>>
    }
    method = <U lambda>
    args = [
    ]
  }
  args = NULL
  body = Integer {
    val = "123"
  }
}

I think the structure reverse part is similar to method calls with block, but I'm not sure if there's a good way to populate the constant receiver. I think we haven't had any similar cases in other nodes?

[amomchilov]

@st0012 I think you can use core::Names::Constants::Kernel() for the receiver, and core::Names::lambda() for the method name.