FIR deserializer: read nullability & add constructors

compiler/fir/resolve/testData/loadCompiledKotlin/fun/nonGeneric/ClassFun.txt

@@ -1,4 +1,6 @@
 public final class River : R|kotlin/Any| {
     public final fun song(): R|kotlin/Int|
 
+    public constructor()
+
 }

compiler/fir/resolve/testData/loadCompiledKotlin/fun/nonGeneric/ClassFunGetFoo.txt

@@ -1,4 +1,6 @@
 public final class ClassFunGetFoo : R|kotlin/Any| {
     public final fun getFoo(): R|kotlin/Int|
 
+    public constructor()
+
 }

compiler/fir/resolve/testData/loadCompiledKotlin/fun/nonGeneric/ClassFunGetFooSetFoo.txt

@@ -3,4 +3,6 @@ public final class ClassFunGetFoo : R|kotlin/Any| {
 
     public final fun setFoo(p: R|kotlin/Int|): R|kotlin/Unit|
 
+    public constructor()
+
 }

compiler/fir/resolve/testData/loadCompiledKotlin/fun/nonGeneric/ClassFunSetFoo.txt

@@ -1,4 +1,6 @@
 public final class ClassFunGetFoo : R|kotlin/Any| {
     public final fun set(p: R|kotlin/Int|): R|kotlin/Unit|
 
+    public constructor()
+
 }

compiler/fir/resolve/testData/loadCompiledKotlin/fun/nonGeneric/ExtFun.txt

@@ -1,2 +1 @@
 public final fun R|kotlin/Int|.shuffle(): R|kotlin/Int|
-

compiler/fir/resolve/testData/loadCompiledKotlin/fun/nonGeneric/ExtFunInClass.txt

@@ -1,4 +1,6 @@
 public final class ExtFunInClass : R|kotlin/Any| {
     public final fun R|kotlin/Int|.shuffle(): R|kotlin/Int|
 
+    public constructor()
+
 }

compiler/fir/resolve/testData/loadCompiledKotlin/fun/nonGeneric/ModifierAbstract.txt

@@ -1,4 +1,6 @@
 public abstract class ModifierAbstract : R|kotlin/Any| {
     public abstract fun abs(): R|kotlin/Int|
 
+    public constructor()
+
 }

compiler/fir/resolve/testData/loadCompiledKotlin/fun/nonGeneric/ModifierOpen.txt

@@ -1,4 +1,6 @@
 public open class ModifierOpen : R|kotlin/Any| {
     public open fun abs(): R|kotlin/Int|
 
+    public constructor()
+
 }

compiler/fir/resolve/testData/loadCompiledKotlin/fun/nonGeneric/ReturnTypeNullable.txt

@@ -1 +1 @@
-public final fun ff(): R|java/lang/Integer|
+public final fun ff(): R|java/lang/Integer|?