[kotlin] Reuse applicability checker between extension candidates

Before, auto-completion was based on on-air resolve, and
'FirTowerDataContext' was computed once, during creation of the
dependent analysis session (with using 'FirTowerDataContextCollector').
This allowed to return the context almost instantly, no matter how many
completion candidates there were.

Dangling file resolution doesn't use 'FirTowerDataContextCollector', as
now there is more precise 'ContextCollector'. However,
'ContextCollector' doesn't cache results by itself, and, if asked, it
will compute the same context over and over again. This exact happened
with extension applicability checker.

The optimized implementation maintains a checker object which caches the
computed context. The old end-point is left to give the IDE plugin time
to adapt to the change.

^KTIJ-28445

analysis/analysis-api/src/org/jetbrains/kotlin/analysis/api/components/KtCompletionCandidateChecker.kt

@@ -5,6 +5,7 @@
 
 package org.jetbrains.kotlin.analysis.api.components
 
+import org.jetbrains.kotlin.analysis.api.KtAnalysisSession
 import org.jetbrains.kotlin.analysis.api.lifetime.KtLifetimeOwner
 import org.jetbrains.kotlin.analysis.api.lifetime.KtLifetimeToken
 import org.jetbrains.kotlin.analysis.api.lifetime.withValidityAssertion
@@ -15,6 +16,13 @@ import org.jetbrains.kotlin.psi.KtFile
 import org.jetbrains.kotlin.psi.KtSimpleNameExpression
 
 public abstract class KtCompletionCandidateChecker : KtAnalysisSessionComponent() {
+    public abstract fun createExtensionCandidateChecker(
+        originalFile: KtFile,
+        nameExpression: KtSimpleNameExpression,
+        explicitReceiver: KtExpression?
+    ): KtCompletionExtensionCandidateChecker
+
+    @Deprecated("Use createExtensionCandidateChecker() instead.")
     public abstract fun checkExtensionFitsCandidate(
         firSymbolForCandidate: KtCallableSymbol,
         originalFile: KtFile,
@@ -23,6 +31,10 @@ public abstract class KtCompletionCandidateChecker : KtAnalysisSessionComponent(
     ): KtExtensionApplicabilityResult
 }
 
+public interface KtCompletionExtensionCandidateChecker {
+    context(KtAnalysisSession)
+    public fun computeApplicability(candidate: KtCallableSymbol): KtExtensionApplicabilityResult
+}
 
 public sealed class KtExtensionApplicabilityResult : KtLifetimeOwner {
     public sealed class Applicable : KtExtensionApplicabilityResult() {
@@ -54,11 +66,36 @@ public sealed class KtExtensionApplicabilityResult : KtLifetimeOwner {
 }
 
 public interface KtCompletionCandidateCheckerMixIn : KtAnalysisSessionMixIn {
+    /**
+     * Returns an extension applicability checker for the given context [nameExpression].
+     * The function is meant to only be used for providing auto-completion for Kotlin in IntelliJ IDEA.
+     *
+     * The returned checker does not cache the results for individual callable candidates.
+     *
+     * @param originalFile The file being edited.
+     * @param nameExpression The expression under the caret in an in-memory copy of [originalFile]
+     *     with a dummy identifier inserted. Also see `CompletionUtilCore.DUMMY_IDENTIFIER` in IntelliJ IDEA.
+     * @param explicitReceiver A receiver expression, if available (also from the in-memory copy of [originalFile]).
+     */
+    public fun createExtensionCandidateChecker(
+        originalFile: KtFile,
+        nameExpression: KtSimpleNameExpression,
+        explicitReceiver: KtExpression?
+    ): KtCompletionExtensionCandidateChecker {
+        return analysisSession.completionCandidateChecker.createExtensionCandidateChecker(
+            originalFile,
+            nameExpression,
+            explicitReceiver
+        )
+    }
+
+    @Deprecated("Use createExtensionCandidateChecker() instead.")
     public fun KtCallableSymbol.checkExtensionIsSuitable(
         originalPsiFile: KtFile,
         psiFakeCompletionExpression: KtSimpleNameExpression,
         psiReceiverExpression: KtExpression?,
     ): KtExtensionApplicabilityResult = withValidityAssertion {
+        @Suppress("DEPRECATION")
         analysisSession.completionCandidateChecker.checkExtensionFitsCandidate(
             this,
             originalPsiFile,