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

fs/registry.go

@@ -8,6 +8,7 @@ import (
 	"fmt"
 	"reflect"
 	"regexp"
+	"slices"
 	"sort"
 	"strings"
 	"sync"
@@ -195,8 +196,8 @@ type Option struct {
 	Help       string           // help, start with a single sentence on a single line that will be extracted for command line help
 	Groups     string           `json:",omitempty"` // groups this option belongs to - comma separated string for options classification
 	Provider   string           `json:",omitempty"` // set to filter on provider
-	Default    interface{}      // default value, nil => "", if set (and not to nil or "") then Required does nothing
-	Value      interface{}      // value to be set by flags
+	Default    any              // default value, nil => "", if set (and not to nil or "") then Required does nothing
+	Value      any              // value to be set by flags
 	Examples   OptionExamples   `json:",omitempty"` // predefined values that can be selected from list (multiple-choice option)
 	ShortOpt   string           `json:",omitempty"` // the short option for this if required
 	Hide       OptionVisibility // set this to hide the config from the configurator or the command line
@@ -232,7 +233,7 @@ func (o *Option) MarshalJSON() ([]byte, error) {
 }
 
 // GetValue gets the current value which is the default if not set
-func (o *Option) GetValue() interface{} {
+func (o *Option) GetValue() any {
 	val := o.Value
 	if val == nil {
 		val = o.Default
@@ -373,7 +374,7 @@ func Register(info *RegInfo) {
 		aliasInfo.Name = alias
 		aliasInfo.Prefix = alias
 		aliasInfo.Hide = true
-		aliasInfo.Options = append(Options(nil), info.Options...)
+		aliasInfo.Options = slices.Clone(info.Options)
 		for i := range aliasInfo.Options {
 			aliasInfo.Options[i].Hide = OptionHideBoth
 		}
@@ -410,7 +411,7 @@ func MustFind(name string) *RegInfo {
 // OptionsInfo holds info about an block of options
 type OptionsInfo struct {
 	Name    string                      // name of this options block for the rc
-	Opt     interface{}                 // pointer to a struct to set the options in
+	Opt     any                         // pointer to a struct to set the options in
 	Options Options                     // description of the options
 	Reload  func(context.Context) error // if not nil, call when options changed and on init
 }