feat(spanner): add spanner::Value support for TypeCode::UUID #15076

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@devbww

The following contributors were found for this pull request:

✅ 967c7cb Author: @devbww <14679271+devbww@users.noreply.github.com>
✅ e87d201 Author: @cuiy0006 <cu***o@google.com>
✅ dc9477d Author: @scotthart <sd***t@google.com>
✅ a8fc7b4 Author: @eliekozah <ek***h@gmail.com>
✅ 2647639 Co-Author: @ddelgrosso1 <85250797+ddelgrosso1@users.noreply.github.com>
✅ 2647639 Author: @eliasdaler <eli*****er@protonmail.com>

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