FIR: support tailrec & external modifiers

compiler/fir/psi2fir/src/org/jetbrains/kotlin/fir/builder/RawFirBuilder.kt

@@ -288,6 +288,8 @@ class RawFirBuilder(val session: FirSession) {
                 function.hasModifier(KtTokens.OPERATOR_KEYWORD),
                 function.hasModifier(KtTokens.INFIX_KEYWORD),
                 function.hasModifier(KtTokens.INLINE_KEYWORD),
+                function.hasModifier(KtTokens.TAILREC_KEYWORD),
+                function.hasModifier(KtTokens.EXTERNAL_KEYWORD),
                 function.receiverTypeReference.convertSafe(),
                 function.typeReference.toFirOrImplicitType(),
                 function.bodyExpression.toFirBody()

compiler/fir/tree/src/org/jetbrains/kotlin/fir/FirRenderer.kt

@@ -119,6 +119,12 @@ class FirRenderer(builder: StringBuilder) : FirVisitorVoid() {
             if (memberDeclaration.isInline) {
                 print("inline ")
             }
+            if (memberDeclaration.isTailRec) {
+                print("tailrec ")
+            }
+            if (memberDeclaration.isExternal) {
+                print("external ")
+            }
         } else if (memberDeclaration is FirProperty) {
             if (memberDeclaration.isConst) {
                 print("const ")

compiler/fir/tree/src/org/jetbrains/kotlin/fir/declarations/FirNamedFunction.kt

@@ -17,6 +17,10 @@ interface FirNamedFunction : @VisitedSupertype FirFunction, FirCallableMember {
 
     val isInline: Boolean
 
+    val isTailRec: Boolean
+
+    val isExternal: Boolean
+
     override fun <R, D> accept(visitor: FirVisitor<R, D>, data: D): R =
         visitor.visitNamedFunction(this, data)
 

compiler/fir/tree/src/org/jetbrains/kotlin/fir/declarations/impl/FirMemberFunctionImpl.kt

@@ -25,6 +25,8 @@ class FirMemberFunctionImpl(
     override val isOperator: Boolean,
     override val isInfix: Boolean,
     override val isInline: Boolean,
+    override val isTailRec: Boolean,
+    override val isExternal: Boolean,
     receiverType: FirType?,
     returnType: FirType,
     override val body: FirBody?