[FIR] Report INAPPLICABLE_INFIX_MODIFIER on vararg parameter, position INAPPLICABLE_INFIX_MODIFIER on infix keyword

#KT-59974

compiler/frontend.common-psi/src/org/jetbrains/kotlin/diagnostics/LightTreePositioningStrategies.kt

@@ -473,6 +473,9 @@ object LightTreePositioningStrategies {
     val OPERATOR_MODIFIER: LightTreePositioningStrategy =
         ModifierSetBasedLightTreePositioningStrategy(KtTokens.OPERATOR_KEYWORD)
 
+    val INFIX_MODIFIER: LightTreePositioningStrategy =
+        ModifierSetBasedLightTreePositioningStrategy(KtTokens.INFIX_KEYWORD)
+
     val ENUM_MODIFIER: LightTreePositioningStrategy =
         ModifierSetBasedLightTreePositioningStrategy(KtTokens.ENUM_KEYWORD)
 

compiler/frontend.common-psi/src/org/jetbrains/kotlin/diagnostics/PositioningStrategies.kt

@@ -315,6 +315,10 @@ object PositioningStrategies {
     val OPERATOR_MODIFIER: PositioningStrategy<KtModifierListOwner> =
         ModifierSetBasedPositioningStrategy(KtTokens.OPERATOR_KEYWORD)
 
+    @JvmField
+    val INFIX_MODIFIER: PositioningStrategy<KtModifierListOwner> =
+        ModifierSetBasedPositioningStrategy(KtTokens.INFIX_KEYWORD)
+
     @JvmField
     val ENUM_MODIFIER: PositioningStrategy<KtModifierListOwner> =
         ModifierSetBasedPositioningStrategy(KtTokens.ENUM_KEYWORD)

compiler/frontend.common-psi/src/org/jetbrains/kotlin/diagnostics/SourceElementPositioningStrategies.kt

@@ -340,6 +340,11 @@ object SourceElementPositioningStrategies {
         PositioningStrategies.OPERATOR_MODIFIER
     )
 
+    val INFIX_MODIFIER = SourceElementPositioningStrategy(
+        LightTreePositioningStrategies.INFIX_MODIFIER,
+        PositioningStrategies.INFIX_MODIFIER
+    )
+
     val NON_FINAL_MODIFIER_OR_NAME = SourceElementPositioningStrategy(
         LightTreePositioningStrategies.NON_FINAL_MODIFIER_OR_NAME,
         PositioningStrategies.NON_FINAL_MODIFIER_OR_NAME