FIR DFA: fix logic clear aliasing

The logic should clear back aliases as well. To ensure all back aliases
don't lose any information, statements on the original variable are
copied over to its aliases.

compiler/testData/diagnostics/tests/smartCasts/variables/aliasing.fir.kt

@@ -0,0 +1,65 @@
+fun test() {
+    var a: Any? = null
+    var b = a
+    var c = b
+    // Now both `b` and `c` are aliases of `a`.
+
+    if (a is String) {
+        b.length // OK
+        c.length // OK
+    }
+    if (b is String) {
+        a.length // OK
+        c.length // OK
+    }
+    if (c is String) {
+        a.length // OK
+        b.length // OK
+    }
+
+    b = 3 // break `b` -> `a`
+    if (a is String) {
+        b.<!UNRESOLVED_REFERENCE!>length<!> // error
+        c.length // OK, since `c` is aliased to `a`
+    }
+    if (b is String) {
+        a.<!UNRESOLVED_REFERENCE!>length<!> // error
+        c.<!UNRESOLVED_REFERENCE!>length<!> // error
+    }
+    if (c is String) {
+        a.length // OK, since `c` is alised to `a`
+        b.<!UNRESOLVED_REFERENCE!>length<!> // error
+    }
+
+    a = 2 // break `c` -> `a`
+    if (a is String) {
+        b.<!UNRESOLVED_REFERENCE!>length<!> // error
+        c.<!UNRESOLVED_REFERENCE!>length<!> // error
+    }
+    if (b is String) {
+        a.<!UNRESOLVED_REFERENCE!>length<!> // error
+        c.<!UNRESOLVED_REFERENCE!>length<!> // error
+    }
+    if (c is String) {
+        a.<!UNRESOLVED_REFERENCE!>length<!> // error
+        b.<!UNRESOLVED_REFERENCE!>length<!> // error
+    }
+
+    c = b // create aliasing `c` -> `b`
+    c.unaryPlus() // OK due to aliasing
+    b = ""
+    c.unaryPlus() // OK since `c` should carry all typing information that was on `b` before `b = ""`.
+
+    c = ""
+    c.length // OK
+    c.<!UNRESOLVED_REFERENCE!>unaryPlus<!>() // error
+}
+
+fun test2() {
+    var a: Any? = null
+    a = ""
+    var b = a
+    a = 3
+    b.length // OK
+    b.<!UNRESOLVED_REFERENCE!>unaryPlus<!>() // error
+}

compiler/testData/diagnostics/tests/smartCasts/variables/aliasing.kt

@@ -0,0 +1,65 @@
+fun test() {
+    var a: Any? = null
+    var b = a
+    var c = b
+    // Now both `b` and `c` are aliases of `a`.
+
+    if (a is String) {
+        b.<!UNRESOLVED_REFERENCE!>length<!> // OK
+        c.<!UNRESOLVED_REFERENCE!>length<!> // OK
+    }
+    if (b is String) {
+        a.<!UNRESOLVED_REFERENCE!>length<!> // OK
+        c.<!UNRESOLVED_REFERENCE!>length<!> // OK
+    }
+    if (c is String) {
+        a.<!UNRESOLVED_REFERENCE!>length<!> // OK
+        b.<!UNRESOLVED_REFERENCE!>length<!> // OK
+    }
+
+    b = 3 // break `b` -> `a`
+    if (a is String) {
+        b.<!UNRESOLVED_REFERENCE!>length<!> // error
+        c.<!UNRESOLVED_REFERENCE!>length<!> // OK, since `c` is aliased to `a`
+    }
+    if (<!USELESS_IS_CHECK!>b is String<!>) {
+        a.<!UNRESOLVED_REFERENCE!>length<!> // error
+        c.<!UNRESOLVED_REFERENCE!>length<!> // error
+    }
+    if (c is String) {
+        a.<!UNRESOLVED_REFERENCE!>length<!> // OK, since `c` is alised to `a`
+        b.<!UNRESOLVED_REFERENCE!>length<!> // error
+    }
+
+    a = 2 // break `c` -> `a`
+    if (<!USELESS_IS_CHECK!>a is String<!>) {
+        b.<!UNRESOLVED_REFERENCE!>length<!> // error
+        c.<!UNRESOLVED_REFERENCE!>length<!> // error
+    }
+    if (<!USELESS_IS_CHECK!>b is String<!>) {
+        a.<!UNRESOLVED_REFERENCE!>length<!> // error
+        c.<!UNRESOLVED_REFERENCE!>length<!> // error
+    }
+    if (c is String) {
+        a.<!UNRESOLVED_REFERENCE!>length<!> // error
+        b.<!UNRESOLVED_REFERENCE!>length<!> // error
+    }
+
+    c = b // create aliasing `c` -> `b`
+    <!DEBUG_INFO_SMARTCAST!>c<!>.unaryPlus() // OK due to aliasing
+    b = ""
+    <!DEBUG_INFO_SMARTCAST!>c<!>.unaryPlus() // OK since `c` should carry all typing information that was on `b` before `b = ""`.
+
+    c = ""
+    <!DEBUG_INFO_SMARTCAST!>c<!>.length // OK
+    c.<!UNRESOLVED_REFERENCE!>unaryPlus<!>() // error
+}
+
+fun test2() {
+    var a: Any? = <!VARIABLE_WITH_REDUNDANT_INITIALIZER!>null<!>
+    a = ""
+    var b = a
+    a = 3
+    <!DEBUG_INFO_SMARTCAST!>b<!>.length // OK
+    b.<!UNRESOLVED_REFERENCE!>unaryPlus<!>() // error
+}

compiler/testData/diagnostics/tests/smartCasts/variables/aliasing.txt

@@ -0,0 +1,4 @@
+package
+
+public fun test(): kotlin.Unit
+public fun test2(): kotlin.Unit

compiler/testData/diagnostics/tests/smartCasts/varnotnull/boundInitializerWrong.fir.kt

@@ -5,7 +5,7 @@ fun foo() {
     val y = x
     x = null
     if (y != null) {
-        x.hashCode()
+        x<!UNSAFE_CALL!>.<!>hashCode()
     }
 }
 

compiler/testData/diagnostics/tests/smartCasts/varnotnull/plusplusMinusminus.fir.kt

@@ -11,7 +11,7 @@ operator fun Long?.inc() = this?.let { it + 1 }
 fun bar(arg: Long?): Long {
     var i = arg
     if (i++ == 5L) {
-        return i<!UNSAFE_CALL!>--<!> + i
+        return i<!UNSAFE_CALL!>--<!> <!UNSAFE_OPERATOR_CALL!>+<!> i
     }
     if (i++ == 7L) {
         return i++ <!UNSAFE_OPERATOR_CALL!>+<!> i