FIR checker/IDE: Add checker and quickfix for WRONG_MODIFIER_TARGET.

There are only simple checks for `external` and `const` for now. The
rest of the checks (see ModifiersChecker in FE1.0) will be added later.

compiler/testData/diagnostics/testsWithStdLib/native/nonFunction.fir.kt

@@ -1,9 +1,9 @@
-external class A
+<!WRONG_MODIFIER_TARGET!>external<!> class A
 
-external val foo: Int = 23
+<!WRONG_MODIFIER_TARGET!>external<!> val foo: Int = 23
 
 class B {
-    external class A
+    <!WRONG_MODIFIER_TARGET!>external<!> class A
 
-    external val foo: Int = 23
+    <!WRONG_MODIFIER_TARGET!>external<!> val foo: Int = 23
 }