For an array access expression e.g., `foo[3]`,
KtFirExpressionTypeProvider first tries
`getReturnTypeForArrayStyleAssignmentTarget(..)` method that determines
the type of the array access expression when it is in the form of "set"
the value. However, the method also returns a non-null result for an
array access expression that reads its value i.e., "get". In this case,
the result of `getKtType()` becomes wrong. This commit lets the method
return a null for the type of "get" array access expression.
Jaebaek Seo
50c293f83f