GH-50720: [C++] Replace std::is_same_v with std::same_as

[dkp116]

Rationale for this change

Upgrade to meet c++20 standards, looking at implementation of same_as on cppref this can be replace is_same_v
https://en.cppreference.com/cpp/concepts/same_as

What changes are included in this PR?

Replace std::is_same_v with std::same_as

Are these changes tested?

Ran testing library, no need to create new test case

Are there any user-facing changes?

No

Was AI used for this PR?

No

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PR code and description written by:

• [ X] Human
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Reviewed before submission by:

• [ X] Human
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• GitHub Issue: [C++] Replace std::is_same_v with std::same_as #50720

[taepper]

Did this change all usages of std::is_same_v in the codebase to std::same_as?

What is the rationale behind this? std::is_same_v is a type trait that evaluates to true or false, while std::same_as is a concept that is used define type constrains. Do you think it is advisable to e.g. replace this also in imperative code within template functions? If so, why?