Add closure support

BrighterScript should support closures.

Here's a quick example:

sub onButtonClick(event)
    response = "" 'gets set by closure below

    checkEmail = (domain) => {
        inputValue = m.emailAddressTextEditBox.text
        if inputValue.endsWith(domain) then
            response ="valid"
        else
            response = "invalid"
        end if
    }

    checkEmail("@roku.com")

    return responseMessage
end sub

would transpile to:

sub onButtonClick(event)
    local = {
        event: event
    }
    local.response = "" 'gets set by closure below

    local.checkEmail = {
        type: "arrow-function",
        scopes: [local],
        m: m,
        func: function(__closure, domain)
            inputValue = __closure.m.emailAddressTextEditBox.text
            if inputValue.endsWith(domain) then
                __closure.scopes[0].response ="valid email"
            else
                __closure.scopes[0].response = "invalid email"
            end if
        end function
    }

    local.checkEmail.func(local.checkEmail, "@roku.com")
    
    return responseMessage
end sub

Considerations:

1. the moment a closure is created, we force all local variables onto an AA, and there are no longer any true local variables. This allows the "local" scope to get "captured" and flow through any child closures
2. since a closure needs type tracking, this can only be implemented in the alpha branch.
3. Add a ArrowFunction interface type which can be used as function parameters and other types.

   sub Validate(validationFunction as ArrowFunction)
       validationFunction() 'transpiles to validationFunction.func(validationFunction)
   end sub
   

4. In the initial release, we will restrict closures from being passed into any parameter/assignment not explicitly marked as ArrowFunction

   sub main()
       arrowFunc = () => { return true }
       name = "bob"
       name = arrowFunc' ERROR: arrow function cannot be assigned to non-closure existing variable
       logInfo(arrowFunc) 'ERROR: arrow function cannot be passed as parameter not explicitly marked as `ArrowFunction`
       callArrowFunc(arrowFunc) ' OK 
       arrowFunc = ()=> {return false} ' OK since previous var was also an arrow function
   end sub
   sub logInfo(anything as dynamic)
       print anything
   end sub
   sub callArrowFunc(func as ArrowFunction)
       func()
   end sub
   

5. Nested closures should be supported. For example:

   sub onButtonClick(event)
       outerName = "outer"
       outerFunc = () =>{
           innerName = "inner"
           print outerName
           innerFunc = () => {
               print outerName; innerName
           }
           innerFunc()
       }
       outerFunc()
   end sub
   

   transpiles to:

   sub onButtonClick(event)
       local = {
           event: event
       }
       local.outerName = "outer"
       local.outerFunc = {
           scopes: [local],
           m: m,
           func: function(__closure)
               local = {}
               local.innerName = "inner"
               print __closure.scopes[0].outerName
               local.innerFunc = {
                   scopes: [__closure.scopes[0], local]
                   m: __closure.scopes[0], 
                   func: function(__closure)
                       print __closure.scopes[0].outerName; __closure.scopes[0].innerName
                   end function
               end function
               local.innerFunc.func(local.innerFunc)
           end func
       }
       local.outerFunc.func(local.outerFunc)
   end sub
   

No implementation files or tests are named. Start on the alpha branch by locating the parser, type-tracking, and transpilation entry points, then compare their current behavior with the closure examples in this issue. Done means supporting captured and nested closures, ArrowFunction typing, and the stated assignment and parameter restrictions.