K2: Extract CheckerContextForProvider from CheckerContext

So, the idea is that CheckerContext should remain just read-only
while the one who runs the checkers might build/modify the context.

^KT-56460 Related

compiler/frontend.common/src/org/jetbrains/kotlin/diagnostics/DiagnosticReporter.kt

@@ -16,15 +16,6 @@ interface DiagnosticContext {
     val languageVersionSettings: LanguageVersionSettings
 }
 
-abstract class MutableDiagnosticContext : DiagnosticContext {
-    abstract fun addSuppressedDiagnostics(
-        diagnosticNames: Collection<String>,
-        allInfosSuppressed: Boolean,
-        allWarningsSuppressed: Boolean,
-        allErrorsSuppressed: Boolean
-    ): DiagnosticContext
-}
-
 abstract class DiagnosticReporter {
     abstract fun report(diagnostic: KtDiagnostic?, context: DiagnosticContext)
 
@@ -97,4 +88,4 @@ open class KtDiagnosticReporterWithContext(
             return result
         }
     }
-}
+}