Remove usages of deprecated VirtualTable.values field

[vbarua]

The Substrait VirtualTable.values is deprecated and set to be removed in substrait-io/substrait#1131.

The DataFusion substrait producer still uses it when producing plans in

datafusion/datafusion/substrait/src/logical_plan/producer/rel/read_rel.rs

Lines 180 to 188 in 37d11af

	ReadType::VirtualTable(VirtualTable {
	// Use deprecated 'values' field instead of 'expressions' because the consumer's
	// nested expression support (RexType::Nested) is not yet implemented.
	// The 'values' field uses literal::Struct which the consumer can properly
	// deserialize with field name preservation.
	#[expect(deprecated)]
	values: vec![LiteralStruct { fields }],
	expressions: vec![],
	})

and

datafusion/datafusion/substrait/src/logical_plan/producer/rel/read_rel.rs

Lines 241 to 244 in 37d11af

	read_type: Some(ReadType::VirtualTable(VirtualTable {
	values,
	expressions,
	})),

Usages of VirtualTable.values should be replaced with VirtualTable.expressions.

[eliot1480]

take