FIR deserializer: read nullability & add constructors

compiler/fir/resolve/testData/loadCompiledKotlin/memberOrder/CallablesNameClash.txt

@@ -11,4 +11,6 @@ public final class A : R|kotlin/Any| {
 
     public final fun c(): R|kotlin/Int|
 
+    public constructor()
+
 }

compiler/fir/resolve/testData/loadCompiledKotlin/memberOrder/EnumEntries.txt

@@ -1,2 +1,4 @@
 public final enum class E : R|kotlin/Enum<test/E>| {
+    private constructor()
+
 }

compiler/fir/resolve/testData/loadCompiledKotlin/memberOrder/ExtensionMembers.txt

@@ -17,4 +17,6 @@ public final class A : R|kotlin/Any| {
 
     public final fun R|kotlin/String|.f3(): R|kotlin/Unit|
 
+    public constructor()
+
 }

compiler/fir/resolve/testData/loadCompiledKotlin/memberOrder/ExtensionPropertiesNameClash.txt

@@ -1,2 +1,4 @@
 public final class A : R|kotlin/Any| {
+    public constructor()
+
 }

compiler/fir/resolve/testData/loadCompiledKotlin/memberOrder/InnerClasses.txt

@@ -1,14 +1,24 @@
 public final class O : R|kotlin/Any| {
+    public constructor()
+
     public final class A1 : R|kotlin/Any| {
+        public constructor()
+
     }
 
     public final inner class A2 : R|kotlin/Any| {
+        public constructor()
+
     }
 
     public final class B1 : R|kotlin/Any| {
+        public constructor()
+
     }
 
     public final inner class B2 : R|kotlin/Any| {
+        public constructor()
+
     }
 
     public abstract interface C1 : R|kotlin/Any| {