[FIR] Downgrade RedundantExplicitTypeChecker to experimental checkers

The checker produces a false positive on integer literals:

```
val it: Long = 0
```

Looks like we don't have the information about how the literal looked
like initially: we have `kind`, but it's replaced when we fix the
literal variable to a specific type with the actual type information,
thus duplicating it. The fix probably deserves a separate refactoring.

^KT-69938

Author: lunakoly

analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/DiagnosticCompilerTestFE10TestdataTestGenerated.java

@@ -8,10 +8,16 @@ package org.jetbrains.kotlin.fir.analysis.checkers
 import org.jetbrains.kotlin.fir.analysis.cfa.FirReturnsImpliesAnalyzer
 import org.jetbrains.kotlin.fir.analysis.checkers.cfa.FirControlFlowChecker
 import org.jetbrains.kotlin.fir.analysis.checkers.declaration.*
+import org.jetbrains.kotlin.fir.analysis.checkers.experimental.RedundantExplicitTypeChecker
 
 object ExperimentalDeclarationCheckers : DeclarationCheckers() {
     override val controlFlowAnalyserCheckers: Set<FirControlFlowChecker>
         get() = setOf(
             FirReturnsImpliesAnalyzer,
         )
+
+    override val propertyCheckers: Set<FirPropertyChecker>
+        get() = setOf(
+            RedundantExplicitTypeChecker,
+        )
 }

analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/LLFirPreresolvedReversedDiagnosticCompilerFE10TestDataTestGenerated.java

@@ -29,8 +29,8 @@ object ExtraDeclarationCheckers : DeclarationCheckers() {
     override val propertyCheckers: Set<FirPropertyChecker>
         get() = setOf(
             RedundantSetterParameterTypeChecker,
-            RedundantExplicitTypeChecker,
         )
+
     override val variableAssignmentCfaBasedCheckers: Set<AbstractFirPropertyInitializationChecker>
         get() = setOf(
             CanBeValChecker,

compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirLightTreeOldFrontendDiagnosticsTestGenerated.java

@@ -1,23 +1,21 @@
 /*
- * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Copyright 2010-2024 JetBrains s.r.o. and Kotlin Programming Language contributors.
  * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
 
-package org.jetbrains.kotlin.fir.analysis.checkers.extra
+package org.jetbrains.kotlin.fir.analysis.checkers.experimental
 
 import org.jetbrains.kotlin.KtFakeSourceElementKind
 import org.jetbrains.kotlin.KtNodeTypes
-import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
-import org.jetbrains.kotlin.fir.analysis.checkers.declaration.FirPropertyChecker
 import org.jetbrains.kotlin.diagnostics.DiagnosticReporter
-import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors
 import org.jetbrains.kotlin.diagnostics.reportOn
 import org.jetbrains.kotlin.fir.analysis.checkers.MppCheckerKind
+import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
+import org.jetbrains.kotlin.fir.analysis.checkers.declaration.FirPropertyChecker
+import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors
 import org.jetbrains.kotlin.fir.declarations.FirProperty
 import org.jetbrains.kotlin.fir.expressions.*
 import org.jetbrains.kotlin.fir.resolve.fullyExpandedType
-import org.jetbrains.kotlin.fir.resolve.toSymbol
-import org.jetbrains.kotlin.fir.symbols.impl.FirTypeAliasSymbol
 import org.jetbrains.kotlin.fir.types.*
 import org.jetbrains.kotlin.name.ClassId
 import org.jetbrains.kotlin.name.Name
@@ -94,4 +92,4 @@ object RedundantExplicitTypeChecker : FirPropertyChecker(MppCheckerKind.Common)
 
     private fun ConeKotlinType.hasSameNameWithoutModifiers(name: Name): Boolean =
         this is ConeClassLikeType && lookupTag.name == name && typeArguments.isEmpty() && !isMarkedNullable
-}
+}

compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirLightTreeOldFrontendDiagnosticsWithLatestLanguageVersionTestGenerated.java

@@ -1,4 +1,4 @@
 $TESTDATA_DIR$/extendedCheckers.kt
--Xuse-fir-extra-checkers
+-Xuse-fir-experimental-checkers
 -d
 $TEMP_DIR$

compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirPsiOldFrontendDiagnosticsTestGenerated.java

@@ -0,0 +1,9 @@
+// WITH_EXPERIMENTAL_CHECKERS
+
+inline fun <T> Iterable<T>.sumByLong(selector: (T) -> Long): Long {
+    var sum: <!REDUNDANT_EXPLICIT_TYPE!>Long<!> = 0
+    for (element in this) {
+        sum += selector(element)
+    }
+    return sum
+}