[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/analysis-api-standalone/analysis-api-standalone-base/src/org/jetbrains/kotlin/analysis/api/standalone/base/project/structure/KtStaticModuleProvider.kt

@@ -8,7 +8,9 @@ package org.jetbrains.kotlin.analysis.api.standalone.base.project.structure
 import com.intellij.psi.PsiElement
 import com.intellij.psi.PsiFileSystemItem
 import org.jetbrains.kotlin.analysis.project.structure.*
+import org.jetbrains.kotlin.analysis.project.structure.impl.KtCodeFragmentModuleImpl
 import org.jetbrains.kotlin.config.LanguageVersionSettings
+import org.jetbrains.kotlin.psi.KtCodeFragment
 import org.jetbrains.kotlin.psi.psiUtil.contains
 import org.jetbrains.kotlin.serialization.deserialization.builtins.BuiltInSerializerProtocol
 import org.jetbrains.kotlin.utils.KotlinExceptionWithAttachments
@@ -23,6 +25,15 @@ class KtStaticModuleProvider(
         // Unwrap context-dependent file copies coming from dependent sessions
         val containingPsiFile = element.containingFile.originalFile
 
+        if (containingPsiFile is KtCodeFragment) {
+            val contextElement = containingPsiFile.context
+                ?: throw KotlinExceptionWithAttachments("Context not found for a code fragment")
+                    .withAttachment("codeFragment.kt", containingPsiFile.text)
+
+            val contextModule = getModule(contextElement, contextualModule)
+            return KtCodeFragmentModuleImpl(containingPsiFile, contextModule)
+        }
+
         val containingVirtualFile = containingPsiFile.virtualFile
         if (containingVirtualFile.extension == BuiltInSerializerProtocol.BUILTINS_FILE_EXTENSION) {
             return builtinsModule