refactor: add comparisons pkg for reused helpers

[displague]

This PR moves the helper functions from provider.go to a new comparisons package. This package will be used by provider, tests, and resources. The refactoring will assist with splitting resources into resource specific packages. #106

The previous helper functions have been deprecated and will be removed in a future commit.

Extracted from #622 (PR grew to large to maintain. Refactoring is not a priority and rebasing gets hard as the underlying code changes)

Related to #674
Related to #654

[displague]

Compared to the original, this function uses generics:

terraform-provider-equinix/equinix/provider.go

Lines 197 to 204 in 3cfe64e

	func stringsFound(source []string, target []string) bool {
	for i := range source {
	if !slices.Contains(target, source[i]) {
	return false
	}
	}
	return true
	}

[displague]

compared to the original, this function uses slices, is more efficient (in ways we won't hit in this project), and is easier to read in my opinion.

terraform-provider-equinix/equinix/provider.go

Lines 232 to 254 in 3cfe64e

	func slicesMatch(s1, s2 []string) bool {
	if len(s1) != len(s2) {
	return false
	}
	visited := make([]bool, len(s1))
	for i := 0; i < len(s1); i++ {
	found := false
	for j := 0; j < len(s2); j++ {
	if visited[j] {
	continue
	}
	if s1[i] == s2[j] {
	visited[j] = true
	found = true
	break
	}
	}
	if !found {
	return false
	}
	}
	return true
	}

[displague]

Tests were taken from https://github.com/equinix/terraform-provider-equinix/blob/comparisons/equinix/provider_test.go#L147-L254

Those tests can be removed with the deprecated functions they test.

[github-actions]

This PR is included in version 2.2.0 🎉