CompileTimeConstantProvider could receive a reference expression,
whose grandparent is KtTypeReference (seen that in UAST inspection).
FIR would not contain anything explicit for this reference,
FirResolvedTypeRef would be received as the nearest parent.
Of course, in this case, there could be no compile time constant anyway.
Support FirStringConcatenationCall in FirCompileTimeConstantEvaluator.
This allows string templates ("foo${bar}") to be evaluated as constants,
assuming the interpolated expressions are themselves constant.
In addition, fixes some handling bugs with KtConstantEvaluationMode,
where some expressions that are not valid in a `const val` declaration
were being supported for `CONSTANT_EXPRESSION_EVALUATION`, including
non-static final Java fields in FIR, and composite expressions of
non-const properties in FE1.0.
Anna Kozlova