all: use Go 1.26 things, run most gofix modernizers

I omitted a lot of the min/max modernizers because they didn't
result in more clear code.

Some of it's older "for x := range 123".

Also: errors.AsType, any, fmt.Appendf, etc.

Updates #18682

Change-Id: I83a451577f33877f962766a5b65ce86f7696471c
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

types/views/views.go

@@ -968,8 +968,8 @@ func containsPointers(typ reflect.Type) bool {
 		if isWellKnownImmutableStruct(typ) {
 			return false
 		}
-		for i := range typ.NumField() {
-			if containsPointers(typ.Field(i).Type) {
+		for field := range typ.Fields() {
+			if containsPointers(field.Type) {
 				return true
 			}
 		}