internal/fwschemadata: Rewrite SetValue semantic equality logic to ignore order

[austinvalle]

Closes #1061

This PR fixes the set semantic equality logic, which prior to this change, was written equivalent to list semantic equality.

Sets are unordered, so to correctly compare the semantic equality of two sets, we must compare each element in the set against all other elements to determine if there is a semantically equivalent element in the set. Once we find a semantically equal element, we remove it from the slice of candidates and continue.

---

As an example, consider a set of case insensitive strings.

With the previous logic, the following sets would be considered semantically equal:

["value-a", "value-b", "value-c"]
["VALUE-A", "VALUE-B", "VALUE-C"]

However the following set would be incorrectly considered semantically not equal, due to the difference in order:

["value-a", "value-b", "value-c"]
["VALUE-B", "VALUE-C", "VALUE-A"]

This change will result in both of these examples being considered semantically equal.

Corner tests

I also wrote some acceptance tests to make it a little easier to understand the impact (using IPv6 address strings as an example)

hashicorp/terraform-provider-corner#297

Unit test failures before the fix

https://github.com/hashicorp/terraform-plugin-framework/actions/runs/12832297072/job/35784696031?pr=1064

--- FAIL: TestValueSemanticEqualitySet (0.00s)
    --- FAIL: TestValueSemanticEqualitySet/SetValue-SetValue-StringValuableWithSemanticEquals-true-diff-order (0.00s)
        value_semantic_equality_set_test.go:1021: unexpected difference:   &fwschemadata.ValueSemanticEqualityResponse{
            - 	NewValue:    s`[["KEEP-LOWERCASE-012","KEEP-LOWERCASE-789"],["KEEP-LOWERCASE-456","KEEP-LOWERCASE-123"]]`,
            + 	NewValue:    s`[["keep-lowercase-123","keep-lowercase-456"],["keep-lowercase-789","keep-lowercase-012"]]`,
              	Diagnostics: nil,
              }
    --- FAIL: TestValueSemanticEqualitySet/SetValue-StringValuableWithSemanticEquals-true-diff-order (0.00s)
        value_semantic_equality_set_test.go:10[21](https://github.com/hashicorp/terraform-plugin-framework/actions/runs/12832297072/job/35784696031?pr=1064#step:5:22): unexpected difference:   &fwschemadata.ValueSemanticEqualityResponse{
            - 	NewValue:    s`["KEEP-LOWERCASE-456","KEEP-LOWERCASE-123"]`,
            + 	NewValue:    s`["keep-lowercase-123","keep-lowercase-456"]`,
              	Diagnostics: nil,
              }

[austinvalle]

Since we have write-only attributes landing soon, this bug fix will go in after in v1.14.1