[Water] Verify Attribute types for WaveExprListAttr

[tgymnich]

Have verifiers for WaveExprListAttr verifying the symbol attributes being either a WaveSymbolAttr or WaveIndexSymbolAttr or both, To avoid
duplication of code like this:

if (!llvm::all_of(lds_load_vector_sizes.getSymbols(), llvm::IsaPred<WaveSymbolAttr, WaveIndexSymbolAttr>)) {
   return emitError() << "lds_load_vector_sizes must only contain WaveSymbolAttr or WaveIndexSymbolAttr";
}

#490 (comment)

Take a look at how Integer attributes use verifiers for a possible solution:
https://github.com/llvm/llvm-project/blob/96c69b7393be845dce997ead88a4cfd3ea0f8944/mlir/include/mlir/IR/CommonAttrConstraints.td#L241-L265