EvaluateAsInitializer does not support evaluating values with dependent
types. This was previously guarded with a check for the initializer
expression, but it is possible for the VarDecl to have a dependent type
without the initializer having a dependent type, when the initializer is
a specialized template type and the VarDecl has the unspecialized type.
This adds a guard checking for dependence in the VarDecl type as well.
This fixes the issue raised by Google in
https://github.com/llvm/llvm-project/pull/145447
