CandidateApplicability: merge INAPPLICABLE_MODIFIER into CONVENTION_ERROR

compiler/fir/analysis-tests/testData/resolve/expresssions/invoke/implicitTypeOrder.fir.txt

@@ -5,7 +5,7 @@ FILE: implicitTypeOrder.kt
         }
 
         public final fun bar(): R|A| {
-            ^bar R|/foo|.<Inapplicable(INAPPLICABLE_MODIFIER): /A.invoke>#()
+            ^bar R|/foo|.<Inapplicable(CONVENTION_ERROR): /A.invoke>#()
         }
 
         public final fun invoke(): R|A| {

compiler/fir/analysis-tests/testData/resolve/qualifierWithCompanion.fir.txt

@@ -26,5 +26,5 @@ FILE: qualifierWithCompanion.kt
         local final fun R|my/A|.invoke(): R|kotlin/Unit| {
         }
 
-        Q|my|.R|my/xx|.<Inapplicable(INAPPLICABLE_MODIFIER): <local>/invoke>#()
+        Q|my|.R|my/xx|.<Inapplicable(CONVENTION_ERROR): <local>/invoke>#()
     }

compiler/fir/semantics/src/org/jetbrains/kotlin/fir/resolve/calls/ResolutionDiagnostic.kt

@@ -119,8 +119,8 @@ class ManyLambdaExpressionArguments(
     val argument: FirExpression
 ) : ResolutionDiagnostic(INAPPLICABLE_ARGUMENTS_MAPPING_ERROR)
 
-class InfixCallOfNonInfixFunction(val function: FirNamedFunctionSymbol) : ResolutionDiagnostic(INAPPLICABLE_MODIFIER)
-class OperatorCallOfNonOperatorFunction(val function: FirNamedFunctionSymbol) : ResolutionDiagnostic(INAPPLICABLE_MODIFIER)
+class InfixCallOfNonInfixFunction(val function: FirNamedFunctionSymbol) : ResolutionDiagnostic(CONVENTION_ERROR)
+class OperatorCallOfNonOperatorFunction(val function: FirNamedFunctionSymbol) : ResolutionDiagnostic(CONVENTION_ERROR)
 
 class InferenceError(val constraintError: ConstraintSystemError) : ResolutionDiagnostic(constraintError.applicability)
 class Unsupported(val message: String, val source: KtSourceElement? = null) : ResolutionDiagnostic(UNSUPPORTED)

compiler/resolution.common/src/org/jetbrains/kotlin/resolve/calls/tower/CandidateApplicability.kt

@@ -13,13 +13,12 @@ enum class CandidateApplicability {
     INAPPLICABLE_WRONG_RECEIVER, // receiver not matched
     INAPPLICABLE_ARGUMENTS_MAPPING_ERROR, // arguments not mapped to parameters (i.e. different size of arguments and parameters)
     INAPPLICABLE, // arguments have wrong types
-    INAPPLICABLE_MODIFIER, // no expected modifier (eg infix call on non-infix function)
     NO_COMPANION_OBJECT, // Classifier does not have a companion object
     IMPOSSIBLE_TO_GENERATE, // access to outer class from nested
     RUNTIME_ERROR, // TODO: FE 1.0 uses this as catch-all for all other errors. Consider re-assigning those diagnostics.
     UNSAFE_CALL, // receiver or argument nullability doesn't match
     UNSTABLE_SMARTCAST, // unstable smart cast
-    CONVENTION_ERROR, // missing infix, operator etc
+    CONVENTION_ERROR, // missing infix, operator etc (= no expected modifier)
 
     // Below has shouldStopResolve = true
     DSL_SCOPE_VIOLATION, // Skip other levels for DSL_SCOPE_VIOLATION because if the candidate is marked DSL_SCOPE_VIOLATION with an inner receiver, one should not keep going to outer receivers.

compiler/testData/diagnostics/tests/BinaryCallsOnNullableValues.fir.kt

@@ -6,7 +6,7 @@ fun f(): Unit {
     var x: Int? = 1
     x = null
     x + 1
-    x <!UNSAFE_INFIX_CALL!>plus<!> 1
+    x <!INFIX_MODIFIER_REQUIRED!>plus<!> 1
     x <!UNSAFE_OPERATOR_CALL!><<!> 1
     <!ASSIGNMENT_TYPE_MISMATCH!>x += 1<!>