validate minimum SPIR-V version for operands

VersionCheck in validate_instruction.cpp checks minimum version for a SPIR-V opcode. But it ignores min-version constraints on operands.

For example, when assembled with --target-env spv1.0, the following should fail validation because StorageBuffer is not in SPIR-V 1.0 core. (StorageBuffer is enabled by SPV_KHR_storage_buffer_storage_class)
```
; SPIR-V
; Version: 1.0
; Generator: Khronos SPIR-V Tools Assembler; 0
; Bound: 3
; Schema: 0
OpCapability Shader
OpCapability Linkage
OpMemoryModel Logical GLSL450
%uint = OpTypeInt 32 0
%_ptr_StorageBuffer_uint = OpTypePointer StorageBuffer %uint
```