lang: Refactor all the highlight helping together

Keep this cleaner and add a bit more.

lang/interpret_test/TestAstFunc1/graph8.txtar

@@ -6,4 +6,4 @@ if true {
 	$b = true
 }
 -- OUTPUT --
-# err: errSetScope: var `$b` does not exist in this scope
+# err: errSetScope: var `$b` does not exist in this scope: /main.mcl @ 2:4-2:5

lang/interpret_test/TestAstFunc1/importscope1.txtar

@@ -16,4 +16,4 @@ class xclass {
 	}
 }
 -- OUTPUT --
-# err: errSetScope: func `os.is_family_debian` does not exist in this scope
+# err: errSetScope: func `os.is_family_debian` does not exist in this scope: /second.mcl @ 5:12-5:33

lang/interpret_test/TestAstFunc2/class-capture7.txtar

@@ -9,4 +9,4 @@ include foo
 # This sort of thing is not currently supported, and not sure if it ever will.
 include bar # nope!
 -- OUTPUT --
-# err: errSetScope: class `bar` does not exist in this scope
+# err: errSetScope: class `bar` does not exist in this scope: /main.mcl @ 9:1-9:12

lang/interpret_test/TestAstFunc2/class-include-as-class2.txtar

@@ -14,4 +14,4 @@ class c1($b) {
 include c1 as i1
 include i1.inner
 -- OUTPUT --
-# err: errSetScope: class `c1` expected 1 args but got 0
+# err: errSetScope: class `c1` expected 1 args but got 0: /main.mcl @ 13:1-13:17

lang/interpret_test/TestAstFunc2/clear-env-on-var.txtar

@@ -7,4 +7,4 @@ $f = func($x) {
 $name = $f("foo")
 test "${name}" {}
 -- OUTPUT --
-# err: errSetScope: var `$x` does not exist in this scope
+# err: errSetScope: var `$x` does not exist in this scope: /main.mcl @ 1:8-1:9

lang/interpret_test/TestAstFunc2/func-gen1.txtar

@@ -11,4 +11,4 @@ include funcgen1
 $x1 = fun1()	# not funcgen1.fun1 since it's *not* an import!
 test "${x1}" {}	# hi
 -- OUTPUT --
-# err: errSetScope: func `fun1` does not exist in this scope
+# err: errSetScope: func `fun1` does not exist in this scope: /main.mcl @ 10:7-10:13

lang/interpret_test/TestAstFunc2/func-gen2.txtar

@@ -14,4 +14,4 @@ include funcgen2
 $x2 = fun2()	# not funcgen2.fun2 since it's *not* an import!
 test "${x2}" {}	# hello world
 -- OUTPUT --
-# err: errSetScope: func `fun2` does not exist in this scope
+# err: errSetScope: func `fun2` does not exist in this scope: /main.mcl @ 13:7-13:13

lang/interpret_test/TestAstFunc2/import-scope-vars2-fail.txtar

@@ -11,4 +11,4 @@ $x = "this is x.mcl"
 import "x.mcl" as f
 $y = $f.x + " and this is y.mcl"
 -- OUTPUT --
-# err: errSetScope: var `$g.x` does not exist in this scope
+# err: errSetScope: var `$g.x` does not exist in this scope: /main.mcl @ 3:6-3:14