Consider activation frame for stack height metering (#2)

* Charge a base cost for calling a function

* Added regression test for empty functions

* Satisfy clippy

tests/expectations/stack-height/empty_functions.wat

@@ -0,0 +1,52 @@
+(module
+  (type (;0;) (func))
+  (func (;0;) (type 0)
+    global.get 0
+    i32.const 2
+    i32.add
+    global.set 0
+    global.get 0
+    i32.const 1024
+    i32.gt_u
+    if  ;; label = @1
+      unreachable
+    end
+    call 0
+    global.get 0
+    i32.const 2
+    i32.sub
+    global.set 0)
+  (func (;1;) (type 0)
+    global.get 0
+    i32.const 2
+    i32.add
+    global.set 0
+    global.get 0
+    i32.const 1024
+    i32.gt_u
+    if  ;; label = @1
+      unreachable
+    end
+    call 0
+    global.get 0
+    i32.const 2
+    i32.sub
+    global.set 0)
+  (func (;2;) (type 0)
+    global.get 0
+    i32.const 2
+    i32.add
+    global.set 0
+    global.get 0
+    i32.const 1024
+    i32.gt_u
+    if  ;; label = @1
+      unreachable
+    end
+    call 1
+    global.get 0
+    i32.const 2
+    i32.sub
+    global.set 0)
+  (global (;0;) (mut i32) (i32.const 0))
+  (export "main" (func 2)))