[klib] Implement diagnostics for clashing KLIB signatures

Now, we detect clashing signatures during serialization to KLIB and
report a compiler error if two or more declarations have the same
`IdSignature`

For example, for the following code:
```kotlin
@Deprecated("", level = DeprecationLevel.HIDDEN)
fun foo(): String = ""

fun foo(): Int = 0
```

the compiler will produce this diagnostic:
```
e: main.kt:1:1 Platform declaration clash: The following declarations
       have the same KLIB signature (/foo|foo(){}[0]):
    fun foo(): String defined in root package
    fun foo(): Int defined in root package
e: main.kt:4:1 Platform declaration clash: The following declarations
       have the same KLIB signature (/foo|foo(){}[0]):
    fun foo(): String defined in root package
    fun foo(): Int defined in root package
```

Note that we report this diagnostic during serialization and not earlier
(e.g., in fir2ir) for more robustness, so ensure that we check
exactly the signatures that will be written to a KLIB.
If we later introduce some annotation for customizing a declaration's
signature (e.g., for preserving binary compatibility), this
diagnostic will continue to work as expected.

^KT-63670 Fixed

native/native.tests/testData/compilerOutput/SignatureClashDiagnostics/main.kt

@@ -0,0 +1,12 @@
+package com.example.klib.serialization.diagnostics
+
+class A {
+    @Deprecated("", level = DeprecationLevel.HIDDEN)
+    fun foo(): String = ""
+
+    fun foo(): Int = 0
+}
+
+fun main() {
+    println(A().foo())
+}

native/native.tests/testData/compilerOutput/SignatureClashDiagnostics/output.txt

@@ -0,0 +1,11 @@
+native/native.tests/testData/compilerOutput/SignatureClashDiagnostics/main.kt:4:5: error: platform declaration clash: The following declarations have the same KLIB signature (com.example.klib.serialization.diagnostics/A.foo|foo(){}[0]):
+    fun foo(): kotlin.String defined in com.example.klib.serialization.diagnostics.A
+    fun foo(): kotlin.Int defined in com.example.klib.serialization.diagnostics.A
+    @Deprecated("", level = DeprecationLevel.HIDDEN)
+    ^
+native/native.tests/testData/compilerOutput/SignatureClashDiagnostics/main.kt:7:5: error: platform declaration clash: The following declarations have the same KLIB signature (com.example.klib.serialization.diagnostics/A.foo|foo(){}[0]):
+    fun foo(): kotlin.String defined in com.example.klib.serialization.diagnostics.A
+    fun foo(): kotlin.Int defined in com.example.klib.serialization.diagnostics.A
+    fun foo(): Int = 0
+    ^
+COMPILATION_ERROR

native/native.tests/tests/org/jetbrains/kotlin/konan/test/blackbox/CompilerOutputTest.kt

@@ -109,7 +109,7 @@ abstract class CompilerOutputTestBase : AbstractNativeSimpleTest() {
         KotlinTestUtils.assertEqualsToFile(goldenData, compilationResult.toOutput())
     }
 
-    private fun compileLibrary(
+    internal fun compileLibrary(
         settings: Settings,
         source: File,
         freeCompilerArgs: List<String> = emptyList(),
@@ -126,7 +126,7 @@ abstract class CompilerOutputTestBase : AbstractNativeSimpleTest() {
         return compilation.result
     }
 
-    private fun TestCompilationResult<*>.toOutput(): String {
+    internal fun TestCompilationResult<*>.toOutput(): String {
         check(this is TestCompilationResult.ImmediateResult<*>) { this }
         val loggedData = this.loggedData
         check(loggedData is LoggedData.CompilationToolCall) { loggedData::class }
@@ -152,4 +152,16 @@ class ClassicCompilerOutputTest : CompilerOutputTestBase()
 @Tag("frontend-fir")
 @TestDataPath("\$PROJECT_ROOT")
 @EnforcedProperty(ClassLevelProperty.COMPILER_OUTPUT_INTERCEPTOR, "NONE")
-class FirCompilerOutputTest : CompilerOutputTestBase()
+class FirCompilerOutputTest : CompilerOutputTestBase() {
+
+    @Test
+    fun testSignatureClashDiagnostics() {
+        // TODO: use the Compiler Core test infrastructure for testing these diagnostics (KT-64393)
+        val rootDir = File("native/native.tests/testData/compilerOutput/SignatureClashDiagnostics")
+        val settings = testRunSettings
+        val compilationResult = compileLibrary(settings, rootDir.resolve("main.kt"))
+        val goldenData = rootDir.resolve("output.txt")
+
+        KotlinTestUtils.assertEqualsToFile(goldenData, compilationResult.toOutput())
+    }
+}