KT-13961 REDECLARATION not reported on private-in-file 'foo' vs public 'foo' in different file

Private-in-file declarations conflict with public overload-equivalent declarations
in other files in the same package.

Move functions for grouping possible redeclarations to OverloadResolver
(since they are used only there).

Refactor redeclarations / conflicting overloads reporting.

jps-plugin/testData/incremental/pureKotlin/classRedeclaration/build.log

@@ -16,4 +16,4 @@ Exit code: ABORT
 ------------------------------------------
 COMPILATION FAILED
 Redeclaration: Klass
-Redeclaration: Klass
+Redeclaration: Klass

jps-plugin/testData/incremental/pureKotlin/funRedeclaration/build.log

@@ -10,4 +10,4 @@ End of files
 Exit code: ABORT
 ------------------------------------------
 COMPILATION FAILED
-'public fun function(): Unit' conflicts with another declaration in package 'test'
+Conflicting overloads: public fun function(): Unit defined in test, public fun function(): Unit defined in test

jps-plugin/testData/incremental/pureKotlin/funVsConstructorOverloadConflict/build.log

@@ -10,4 +10,4 @@ End of files
 Exit code: ABORT
 ------------------------------------------
 COMPILATION FAILED
-'public constructor function()' conflicts with another declaration in package 'test'
+Conflicting overloads: public constructor function() defined in test.function, public fun function(): Unit defined in test

jps-plugin/testData/incremental/pureKotlin/propertyRedeclaration/build.log

@@ -10,4 +10,4 @@ End of files
 Exit code: ABORT
 ------------------------------------------
 COMPILATION FAILED
-Redeclaration: property
+Conflicting declarations: public val property: Int, public val property: Int