This was broken out of #782 since it involves a widely-used helper
function and will impact more than just the Metal VLAN resource.

Previously, the `IgnoreHttpResponseErrors` helper function accepted as
arguments a number of other, existing helper functions that are meant to
evaluate whether a particular API response has a certain HTTP status.
Here's [an example helper function for checking if the response is a
403](https://github.com/equinix/terraform-provider-equinix/blob/b1ed71b389705513308c1e47e7ac6ff0c46891cd/internal/errors/errors.go#L119-L130):

```go
func HttpForbidden(resp *http.Response, err error) bool {
	if resp != nil && (resp.StatusCode != http.StatusForbidden) {
		return false
	}

	switch err := err.(type) {
	case *ErrorResponse, *packngo.ErrorResponse:
		return IsForbidden(err)
	}

	return false
}
```

This function immediately returns false if the response status code _is
not_ 403; otherwise it tries to convert the error argument to an
`ErrorResponse` or a `packngo.ErrorResponse` and then use a different
helper function to determine if that error represents a 403. This
assumes that the error object contains a copy of the response, which is
only certain to be the case for code that uses `packngo`. In practice we
almost never did the necessary conversion to `ErrorResponse` for
non-`packngo` resources and data sources, so in many cases we were
probably not successfully ignoring the desired response codes.

This refactors `IgnoreHttpResponseErrors` to inspect HTTP status codes
directly in the response instead of relying on helper functions for
specific custom error types.

This also removes the `FriendlyErrorForMetalGo` function which only
existed in order to convert a separate HTTP response and error into an
`ErrorResponse`, which is no longer necessary. Some usage of
`FriendlyError` is also removed in cases where that function had no or
minimal effect.

This was broken out of equinix#782 since it involves a widely-used helper
function and will impact more than just the Metal VLAN resource.

Previously, the `IgnoreHttpResponseErrors` helper function accepted as
arguments a number of other, existing helper functions that are meant to
evaluate whether a particular API response has a certain HTTP status.
Here's [an example helper function for checking if the response is a
403](https://github.com/equinix/terraform-provider-equinix/blob/b1ed71b389705513308c1e47e7ac6ff0c46891cd/internal/errors/errors.go#L119-L130):

```go
func HttpForbidden(resp *http.Response, err error) bool {
	if resp != nil && (resp.StatusCode != http.StatusForbidden) {
		return false
	}

	switch err := err.(type) {
	case *ErrorResponse, *packngo.ErrorResponse:
		return IsForbidden(err)
	}

	return false
}
```

This function immediately returns false if the response status code _is
not_ 403; otherwise it tries to convert the error argument to an
`ErrorResponse` or a `packngo.ErrorResponse` and then use a different
helper function to determine if that error represents a 403. This
assumes that the error object contains a copy of the response, which is
only certain to be the case for code that uses `packngo`. In practice we
almost never did the necessary conversion to `ErrorResponse` for
non-`packngo` resources and data sources, so in many cases we were
probably not successfully ignoring the desired response codes.

This refactors `IgnoreHttpResponseErrors` to inspect HTTP status codes
directly in the response instead of relying on helper functions for
specific custom error types.

This also removes the `FriendlyErrorForMetalGo` function which only
existed in order to convert a separate HTTP response and error into an
`ErrorResponse`, which is no longer necessary. Some usage of
`FriendlyError` is also removed in cases where that function had no or
minimal effect.