build: modernize Go usage

This commit modernizes Go usage. This was done with:

go run golang.org/x/tools/gopls/internal/analysis/modernize/cmd/modernize@latest -fix -test ./...

Then files needed to be `go fmt`ed and a few comments needed to be
restored.

The modernizations include replacing

- if/else conditional assignment by a call to the built-in min or max functions added in go1.21
- sort.Slice(x, func(i, j int) bool) { return s[i] < s[j] } by a call to slices.Sort(s), added in go1.21
- interface{} by the 'any' type added in go1.18
- append([]T(nil), s...) by slices.Clone(s) or slices.Concat(s), added in go1.21
- loop around an m[k]=v map update by a call to one of the Collect, Copy, Clone, or Insert functions from the maps package, added in go1.21
- []byte(fmt.Sprintf...) by fmt.Appendf(nil, ...), added in go1.19
- append(s[:i], s[i+1]...) by slices.Delete(s, i, i+1), added in go1.21
- a 3-clause for i := 0; i < n; i++ {} loop by for i := range n {}, added in go1.22

backend/b2/api/types.go

@@ -130,10 +130,10 @@ type AuthorizeAccountResponse struct {
 	AbsoluteMinimumPartSize int      `json:"absoluteMinimumPartSize"` // The smallest possible size of a part of a large file.
 	AccountID               string   `json:"accountId"`               // The identifier for the account.
 	Allowed                 struct { // An object (see below) containing the capabilities of this auth token, and any restrictions on using it.
-		BucketID     string      `json:"bucketId"`     // When present, access is restricted to one bucket.
-		BucketName   string      `json:"bucketName"`   // When present, name of bucket - may be empty
-		Capabilities []string    `json:"capabilities"` // A list of strings, each one naming a capability the key has.
-		NamePrefix   interface{} `json:"namePrefix"`   // When present, access is restricted to files whose names start with the prefix
+		BucketID     string   `json:"bucketId"`     // When present, access is restricted to one bucket.
+		BucketName   string   `json:"bucketName"`   // When present, name of bucket - may be empty
+		Capabilities []string `json:"capabilities"` // A list of strings, each one naming a capability the key has.
+		NamePrefix   any      `json:"namePrefix"`   // When present, access is restricted to files whose names start with the prefix
 	} `json:"allowed"`
 	APIURL              string `json:"apiUrl"`              // The base URL to use for all API calls except for uploading and downloading files.
 	AuthorizationToken  string `json:"authorizationToken"`  // An authorization token to use with all calls, other than b2_authorize_account, that need an Authorization header.