KT-57468 Kotlin assignment plugin: operation name cannot be found

The problem results in broken import quick fix and import optimizer on
the IDE side [1].

`AssignResolutionAltererExtension` introduced a possibility to override
 resolution of assignment statements. The inconsistency though is
 that `KtSimpleNameReference.getResolvesByNames` doesn't return a name
 for the overridden `=`. Kotlin as a language doesn't support this [2].

This commit eliminates the drawback above:
1. It fixes the name `assign` the `=` can be resolved to [3].
   This eliminates the need to search for the name, bypassing the
   plugins.
2. `KtSimpleNameReference.getResolvesByNames` returns `assign` among
   other names in case it deals with binary `=` and assignment is
   resolved.
3. `KtCompilerPluginsProvider` was extended to check plugins' presence.
   K1 implementation added.

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[1]: https://youtrack.jetbrains.com/issue/KTIJ-24390
[2]: OperatorConventions.getNameForOperationSymbol
     https://kotlinlang.org/docs/operator-overloading.html#augmented-assignments
[3]: OperatorConventions#ASSIGN_METHOD + AssignmentPluginNames

compiler/psi/src/org/jetbrains/kotlin/types/expressions/OperatorConventions.java

@@ -104,6 +104,8 @@ public class OperatorConventions {
             .put(KtTokens.MINUSEQ, KtTokens.MINUS)
             .build();
 
+    public static final Name ASSIGN_METHOD = Name.identifier("assign");
+
     public static final ImmutableBiMap<KtSingleValueToken, Name> BOOLEAN_OPERATIONS = ImmutableBiMap.<KtSingleValueToken, Name>builder()
              .put(KtTokens.ANDAND, AND)
              .put(KtTokens.OROR, OR)