Get rid of duplicated file names in spec tests

Otherwise, corresponding IDE tests would fail on creation duplicated
files in the same directory

compiler/tests-spec/testData/diagnostics/linked/expressions/constant-literals/the-types-for-integer-literals/p-1/pos/2.5.kt

@@ -11,7 +11,7 @@
  * HELPERS: checkType
  */
 
-// FILE: functions.kt
+// FILE: fileWithFunctions.kt
 
 package functions
 

compiler/tests-spec/testData/diagnostics/linked/expressions/prefix-expressions/prefix-increment-expression/p-4/neg/1.1.kt

@@ -13,7 +13,7 @@
  */
 
 
-// FILE: TestCase.kt
+// FILE: TestCase1.kt
 // TESTCASE NUMBER: 1
 package testPackCase1
 
@@ -36,7 +36,7 @@ class Case1() {
     var a: A = A()
 }
 
-// FILE: TestCase.kt
+// FILE: TestCase2.kt
 // TESTCASE NUMBER: 2
 package testPackCase2
 

compiler/tests-spec/testData/diagnostics/linked/expressions/try-expression/p-8/neg/1.1.kt

@@ -12,7 +12,7 @@
  * DESCRIPTION: The type of the try-expression is the least upper bound of the types of the last expressions of the try body and the last expressions of all the catch blocks
  */
 
-// FILE: TestCase.kt
+// FILE: TestCase1.kt
 // TESTCASE NUMBER: 1
 package testPackCase1
 
@@ -38,7 +38,7 @@ fun case1() {
     }
 }
 
-// FILE: TestCase.kt
+// FILE: TestCase2.kt
 // TESTCASE NUMBER: 2
 package testPackCase2
 
@@ -66,7 +66,7 @@ fun case2() {
 }
 
 
-// FILE: TestCase.kt
+// FILE: TestCase3.kt
 // TESTCASE NUMBER: 3
 // ISSUES: KT-35494
 package testPackCase3