FIR: Reimplement conflicts checker to detect conflicts in different files

also pass correct ScopeSession to checkers
fixes some IC tests

compiler/testData/diagnostics/tests/redeclarations/ClassRedeclarationInDifferentFiles.fir.kt

@@ -1,11 +1,11 @@
 // FILE: f1.kt
 package test
 
-class A
+<!REDECLARATION!>class A<!>
 class F1
 
 // FILE: f2.kt
 package test
 
-class A
+<!REDECLARATION!>class A<!>
 class F2

compiler/testData/diagnostics/tests/redeclarations/FunVsCtorInDifferentFiles.fir.kt

@@ -1,10 +0,0 @@
-// FILE: test1.kt
-class A
-class B(val x: Int) {
-    constructor(x: Int, y: Int): this(x + y)
-}
-
-// FILE: test2.kt
-fun A() {}
-fun B(x: Int) = x
-fun B(x: Int, y: Int) = x + y

compiler/testData/diagnostics/tests/redeclarations/FunVsCtorInDifferentFiles.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 // FILE: test1.kt
 class <!CONFLICTING_OVERLOADS!>A<!>
 class B<!CONFLICTING_OVERLOADS!>(val x: Int)<!> {

compiler/testData/diagnostics/tests/redeclarations/RedeclarationInMultiFile.fir.kt

@@ -1,9 +1,9 @@
 // FILE: a.kt
-val a : Int = 1
-fun f() {
+<!REDECLARATION!>val a : Int = 1<!>
+<!CONFLICTING_OVERLOADS!>fun f()<!> {
 }
 
 // FILE: b.kt
-val a : Int = 1
-fun f() {
+<!REDECLARATION!>val a : Int = 1<!>
+<!CONFLICTING_OVERLOADS!>fun f()<!> {
 }

compiler/testData/diagnostics/tests/redeclarations/RedeclaringPrivateToFile.fir.kt

@@ -7,8 +7,8 @@ interface B : A
 private fun validFun() {}
 private val validVal = 1
 
-private fun invalidFun0() {}
-private val invalidProp0 = 1
+<!CONFLICTING_OVERLOADS!>private fun invalidFun0()<!> {}
+<!REDECLARATION!>private val invalidProp0 = 1<!>
 
 // NB invalidFun0 and invalidProp0 are conflicting overloads, since the following is an ambiguity:
 fun useInvalidFun0() = invalidFun0()
@@ -20,7 +20,7 @@ fun useInvalidProp0() = invalidProp0
 <!CONFLICTING_OVERLOADS!>private fun invalidFun2()<!> {}
 <!CONFLICTING_OVERLOADS!>public fun invalidFun2()<!> {}
 
-public fun invalidFun3() {}
+<!CONFLICTING_OVERLOADS!>public fun invalidFun3()<!> {}
 
 <!CONFLICTING_OVERLOADS!>private fun invalidFun4()<!> {}
 <!CONFLICTING_OVERLOADS!>public fun invalidFun4()<!> {}
@@ -34,16 +34,16 @@ package a
 private fun validFun() {}
 private val validVal = 1
 
-private fun invalidFun0() {}
+<!CONFLICTING_OVERLOADS!>private fun invalidFun0()<!> {}
 
-private val invalidProp0 = 1
+<!REDECLARATION!>private val invalidProp0 = 1<!>
 
-internal fun invalidFun3() {}
-internal fun invalidFun4() {}
+<!CONFLICTING_OVERLOADS!>internal fun invalidFun3()<!> {}
+<!CONFLICTING_OVERLOADS!>internal fun invalidFun4()<!> {}
 
 // FILE: c.kt
 package a
 
 public fun invalidFun0() {}
 
-public val invalidProp0 = 1
+public val invalidProp0 = 1

compiler/testData/diagnostics/tests/redeclarations/TypeAliasVsClass.fir.kt

@@ -15,4 +15,4 @@ class Outer {
 }
 
 // FILE: file2.kt
-typealias SomeClass = Any
+<!REDECLARATION!>typealias SomeClass = Any<!>

compiler/testData/diagnostics/tests/typealias/privateInFile.fir.kt

@@ -18,5 +18,5 @@ private val test1co: C.Companion = C
 private val test2: TA = <!INAPPLICABLE_CANDIDATE!>TA<!>()
 private val test2co = TA
 
-private class C
-private typealias TA = Int
+<!REDECLARATION!>private class C<!>
+<!REDECLARATION!>private typealias TA = Int<!>