[FIR] Support 4 diagnostics for pairs of modifiers

In particular, this commit includes:
* Attempt to abstract access to FirSourceElement via FirModifier
* Add more visit functions to DeclarationCheckersDiagnosticComponent
* Add messages+factories for 4 modifier-related errors and warnings
* Introduce FirModifierChecker

compiler/testData/diagnostics/tests/annotations/rendering/cannotOverrideInvisibleMember.fir.kt

@@ -7,7 +7,7 @@ annotation class A
 @A
 open class B1 {
     @A
-    private open fun foo() {}
+    <!INCOMPATIBLE_MODIFIERS!>private<!> <!INCOMPATIBLE_MODIFIERS!>open<!> fun foo() {}
 }
 
 class D1 : B1() {