[IR] Add the description field to CommonIdSignature

This field shall be used for storing a human-readable representation
of the declaration, that would be a mangled name for now.

This field is not yet serialized. Serialization will be implemented in
follow-up commits.

See KT-59486

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/types/irTypePredicates.kt

@@ -45,14 +45,26 @@ object IdSignatureValues {
     @JvmField val iterable = getPublicSignature(StandardNames.COLLECTIONS_PACKAGE_FQ_NAME, "Iterable")
     @JvmField val continuation = getPublicSignature(StandardNames.COROUTINES_PACKAGE_FQ_NAME, "Continuation")
     @JvmField val result = getPublicSignature(StandardNames.BUILT_INS_PACKAGE_FQ_NAME, "Result")
-    @JvmField val sequence = IdSignature.CommonSignature("kotlin.sequences", "Sequence", null, 0)
+    @JvmField val sequence = IdSignature.CommonSignature(
+        packageFqName = "kotlin.sequences",
+        declarationFqName = "Sequence",
+        id = null,
+        mask = 0,
+        description = "kotlin.sequences.Sequence",
+    )
 }
 
 private fun IrType.isNotNullClassType(signature: IdSignature.CommonSignature) = isClassType(signature, nullable = false)
 private fun IrType.isNullableClassType(signature: IdSignature.CommonSignature) = isClassType(signature, nullable = true)
 
 fun getPublicSignature(packageFqName: FqName, name: String) =
-    IdSignature.CommonSignature(packageFqName.asString(), name, null, 0)
+    IdSignature.CommonSignature(
+        packageFqName = packageFqName.asString(),
+        declarationFqName = name,
+        id = null,
+        mask = 0,
+        description = packageFqName.child(Name.identifier(name)).asString(),
+    )
 
 private fun IrType.isClassType(signature: IdSignature.CommonSignature, nullable: Boolean? = null): Boolean {
     if (this !is IrSimpleType) return false

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/IdSignature.kt

@@ -266,8 +266,17 @@ sealed class IdSignature {
 
     /**
      * This signature corresponds to a publicly accessible Kotlin declaration.
+     *
+     * @property description This property does not affect linkage and is used only for showing humnan-readable error messages.
+     * Note: currently, we store here the mangled name from which [id] was computed. Later we can reconsider.
      */
-    class CommonSignature(val packageFqName: String, val declarationFqName: String, val id: Long?, val mask: Long) : IdSignature() {
+    class CommonSignature(
+        val packageFqName: String,
+        val declarationFqName: String,
+        val id: Long?,
+        val mask: Long,
+        val description: String?,
+    ) : IdSignature() {
         override val isPubliclyVisible: Boolean get() = true
 
         override fun packageFqName(): FqName = FqName(packageFqName)
@@ -295,7 +304,13 @@ sealed class IdSignature {
             val adaptedMask = adaptMask(mask)
             if (nameSegments.size == 1 && mask == adaptedMask) return this
 
-            return CommonSignature(packageFqName, nameSegments.first(), null, adaptedMask)
+            return CommonSignature(
+                packageFqName = packageFqName,
+                declarationFqName = nameSegments.first(),
+                id = null,
+                mask = adaptedMask,
+                description = null
+            )
         }
 
         override fun isPackageSignature(): Boolean = id == null && declarationFqName.isEmpty()