[compute] Apply std::variant to Shape

[ragmani]

This applies std::variant to replace in the union in Shape.

ONE-DCO-1.0-Signed-off-by: ragmani [email protected]

[ragmani]

This approach leverages automatic memory management provided by std::variant and avoids the potential pitfalls of manually managing memory with a union.

Before the Change:

The original code used a union to store internal data: if the shape size was less than or equal to kMaxSmallSize, it was stored in a fixed-size array (_dims); otherwise, it was stored in a dynamically allocated pointer (_dims_pointer).

After the Change:

The union is replaced with a std::variant so that the internal data is stored as follows:

When the shape size is less than or equal to kMaxSmallSize, it uses std::array<int32_t, kMaxSmallSize>.

When the shape size is larger, it uses std::vector<int32_t>.

Key Modifications:

The member variable _dims is now declared as
std::variant<std::array<int32_t, kMaxSmallSize>, std::vector<int32_t>> instead of a union.

The constructors, Dims(), SetDim(), DimsData(), Resize(), and ReplaceWith() functions have been updated to use the std::variant access methods instead of direct union access.

The rest of the functions remain largely unchanged, preserving the original comments and functionality.

[ragmani]

Generally, there is no strict requirement to mark a function template as inline. Template functions (especially non-member ones) already avoid multiple-definition errors due to how templates are instantiated and handled by the compiler. Marking it inline usually does no harm, but it’s not strictly necessary in this situation. Nevertheless, I added it for code consistency.

[ragmani]

This PR might negatively affect latency, so I discard it.