spirv-val: Missing transform feedback validation around Offset in the output variable

[spencer-lunarg]

• VUID-StandaloneSpirv-Offset-04687
• VUID-StandaloneSpirv-Offset-04689
• VUID-StandaloneSpirv-Offset-04690
• VUID-StandaloneSpirv-Offset-04691
• VUID-StandaloneSpirv-Offset-04692
• VUID-StandaloneSpirv-Offset-04716
• VUID-StandaloneSpirv-Offset-04865

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Other Transform feedback missing checks

• VUID-StandaloneSpirv-Stream-04694
• VUID-StandaloneSpirv-XfbBuffer-04693
• VUID-StandaloneSpirv-XfbBuffer-04696
• VUID-StandaloneSpirv-XfbBuffer-04697

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somewhat related - #6630