[LL API] Analyze code fragment in a separate 'FirSession'

Before, `KtCodeFragment`/`FirCodeFragment` was analyzed as a part of
its context `KtModule`. This has the following complications:

- In non-source sessions, diagnostic reporting is globally disabled.
  For code fragments, however, checking the code before passing it to
  the backend is essential.

- Special treatment for call ambiguities in libraries
  (`LLLibraryScopeAwareCallConflictResolverFactory`) becomes complicated
  as the conflict resolver has to be applied to a library module.

- `KtCodeFragment`s usually have a shorter lifetime than their own
  context. Caching may potentially be implemented differently for them.

^KT-61783 Fixed

analysis/project-structure/src/org/jetbrains/kotlin/analysis/project/structure/KtModule.kt

@@ -10,6 +10,7 @@ import com.intellij.psi.PsiFile
 import com.intellij.psi.search.GlobalSearchScope
 import org.jetbrains.kotlin.config.LanguageVersionSettings
 import org.jetbrains.kotlin.platform.TargetPlatform
+import org.jetbrains.kotlin.psi.KtCodeFragment
 import org.jetbrains.kotlin.psi.KtFile
 import org.jetbrains.kotlin.resolve.PlatformDependentAnalyzerServices
 import java.nio.file.Path
@@ -214,6 +215,24 @@ public interface KtScriptDependencyModule : KtModule {
     public val file: KtFile?
 }
 
+/**
+ * A module for a Kotlin code fragment – a piece of code analyzed against a specific context element.
+ */
+public interface KtCodeFragmentModule : KtModule {
+    /**
+     * A code fragment PSI.
+     */
+    public val codeFragment: KtCodeFragment
+
+    /**
+     * Module of the context element.
+     */
+    public val contextModule: KtModule
+
+    override val moduleDescription: String
+        get() = "Code fragment"
+}
+
 /**
  * A set of sources which live outside the project content root. E.g, testdata files or source files of some other project.
  */

analysis/project-structure/src/org/jetbrains/kotlin/analysis/project/structure/impl/KtCodeFragmentModuleImpl.kt

@@ -0,0 +1,58 @@
+/*
+ * Copyright 2010-2023 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.analysis.project.structure.impl
+
+import com.intellij.openapi.project.Project
+import com.intellij.psi.search.GlobalSearchScope
+import org.jetbrains.kotlin.analysis.project.structure.KtCodeFragmentModule
+import org.jetbrains.kotlin.analysis.project.structure.KtModule
+import org.jetbrains.kotlin.platform.TargetPlatform
+import org.jetbrains.kotlin.psi.KtCodeFragment
+import org.jetbrains.kotlin.resolve.PlatformDependentAnalyzerServices
+import java.util.Objects
+
+public class KtCodeFragmentModuleImpl(
+    override val codeFragment: KtCodeFragment,
+    override val contextModule: KtModule
+) : KtCodeFragmentModule {
+    override val project: Project
+        get() = contextModule.project
+
+    override val platform: TargetPlatform
+        get() = contextModule.platform
+
+    override val analyzerServices: PlatformDependentAnalyzerServices
+        get() = contextModule.analyzerServices
+
+    override val contentScope: GlobalSearchScope
+        get() = GlobalSearchScope.fileScope(codeFragment)
+
+    override val directRegularDependencies: List<KtModule>
+        get() = contextModule.directRegularDependencies
+
+    override val directDependsOnDependencies: List<KtModule>
+        get() = contextModule.directDependsOnDependencies
+
+    override val directFriendDependencies: List<KtModule>
+        get() = listOf(contextModule) + contextModule.directFriendDependencies
+
+    override val transitiveDependsOnDependencies: List<KtModule>
+        get() = contextModule.transitiveDependsOnDependencies
+
+    override fun equals(other: Any?): Boolean {
+        if (this === other) return true
+
+        if (other is KtCodeFragmentModuleImpl) {
+            return codeFragment == other.codeFragment && contextModule == other.contextModule
+        }
+
+        return false
+    }
+
+    override fun hashCode(): Int {
+        return Objects.hash(codeFragment, contextModule)
+    }
+}