lang: ast, parser: Allow calling anonymous functions

I forgot to plumb this in through the parser. Pretty easy to add,
hopefully I didn't forget any weird corner scope cases here.

lang/interpret_test/TestAstFunc2/call-inline-lambda1.txtar

@@ -0,0 +1,8 @@
+-- main.mcl --
+$s = func() {
+	"hello"
+}() # inline lambda call
+
+test [$s,] {}
+-- OUTPUT --
+Vertex: test[hello]

lang/interpret_test/TestAstFunc2/call-inline-lambda2.txtar

@@ -0,0 +1,8 @@
+-- main.mcl --
+$s = func($x) {
+	"hello" + $x
+}("world") # inline lambda call
+
+test [$s,] {}
+-- OUTPUT --
+Vertex: test[helloworld]

lang/interpret_test/TestAstFunc2/call-inline-lambda3.txtar

@@ -0,0 +1,10 @@
+-- main.mcl --
+import "fmt"
+
+$s = fmt.printf("%v", func($x) {
+	len($x)
+}("helloworld")) # inline lambda call
+
+test [$s,] {}
+-- OUTPUT --
+Vertex: test[10]

lang/interpret_test/TestAstFunc2/call-inline-lambda4.txtar

@@ -0,0 +1,10 @@
+-- main.mcl --
+import "fmt"
+
+$s = fmt.printf("%v", func($x) {
+	len($x)
+}(func($x){ $x }("helloworld"))) # inline lambda call as an arg to another
+
+test [$s,] {}
+-- OUTPUT --
+Vertex: test[10]