fix: preserve vararg info in recursive function definition

Fixes #727

spec/call/function_spec.lua

@@ -11,4 +11,25 @@ describe("function calls", function()
    ]], {
       { y = 6, msg = "variable is not being assigned a value" },
    }))
+
+   it("can perform recursive calls on varargs (regression test for #727)", util.check([[
+      local message:string = "hello world!"
+
+      local function foo(...: string): string
+          local n = select("#", ...)
+          if n < 3 then
+              return ""
+          end
+          if message ~= "hello world" then
+              return foo("hi there", select(2, ...))
+          else
+              local r = {"hi there", select(2, ...)}
+              return foo(table.unpack(r))
+          end
+      end
+
+      local function bar(...: string): string
+          return foo("hi there", select(2, ...))
+      end
+   ]]))
 end)

tl.lua

@@ -7918,7 +7918,7 @@ tl.type_check = function(ast, opts)
    end
 
    local function add_function_definition_for_recursion(node)
-      local args = a_type({ typename = "tuple" })
+      local args = a_type({ typename = "tuple", is_va = node.args.type.is_va })
       for _, fnarg in ipairs(node.args) do
          table.insert(args, fnarg.type)
       end

tl.tl

@@ -7918,7 +7918,7 @@ tl.type_check = function(ast: Node, opts: TypeCheckOptions): Result, string
    end
 
    local function add_function_definition_for_recursion(node: Node)
-      local args: Type = a_type { typename = "tuple" }
+      local args: Type = a_type { typename = "tuple", is_va = node.args.type.is_va }
       for _, fnarg in ipairs(node.args) do
          table.insert(args, fnarg.type)
       end