Goal of this PR
We want to support an array whose size can be specialization constant for shared/global variable e.g.

layout (constant_id = 0) const uint BLOCK_SIZE = 64;
shared float buf_a[(BLOCK_SIZE + 5) * 4];

Overview of the solution:

• During IndexExpr check, we will loose the restriction to allow SpecConst passing, but the size parameter will not be a constant value because it cannot be folded into a constant, instead it will be an expression that will result in SpecConst value.
• During IR lowering, we will still lower the array to sized array, but the size will not be an int value, instead we will lower it to a global constant, the initial value will be the IR inst lowering from the specConst expression from above step, and we will decorate this global constant variable with kIROp_SpecializationConstantOpDecoration.
• During spirv emit stage, we will allow emit global constant variable only when it has the decoration of kIROp_SpecializationConstantOpDecoration.
• We have to implement new logic to emit OpSpecConstantOp, the existing emit logic doesn't support emitting OpSpecConstantOp, especially this op can embed arithmetic operation at global scope, where we can only emit arithmetic instruct at local. But there are only few instructs we need to support.

Overview of the solution:
Note: This PR is not aimed to support all possible opcodes supported by OpSpecConstantOp, only those 32-bit integer opcode, because only those types can be used for array size. For those untypical usage, we can leave in the future to extend, current emit struct should be easy to extend.