tailcfg: add location field to hostinfo

This change adds Location field to HostInfo.
Location contains the option for a Country, CountryCode, City, CityCode
and a Priority. Neither of these fields are populated by default.

The Priority field is used to determine the priority an exit
node should be given for use, if the field is set. The higher the value
set, the higher priority the node should be given for use.

Updates tailscale/corp#12146

Signed-off-by: Charlotte Brandhorst-Satzkorn <charlotte@tailscale.com>

tailcfg/tailcfg_clone.go

@@ -119,6 +119,10 @@ func (src *Hostinfo) Clone() *Hostinfo {
 	dst.Services = append(src.Services[:0:0], src.Services...)
 	dst.NetInfo = src.NetInfo.Clone()
 	dst.SSH_HostKeys = append(src.SSH_HostKeys[:0:0], src.SSH_HostKeys...)
+	if dst.Location != nil {
+		dst.Location = new(Location)
+		*dst.Location = *src.Location
+	}
 	return dst
 }
 
@@ -157,6 +161,7 @@ var _HostinfoCloneNeedsRegeneration = Hostinfo(struct {
 	Cloud           string
 	Userspace       opt.Bool
 	UserspaceRouter opt.Bool
+	Location        *Location
 }{})
 
 // Clone makes a deep copy of NetInfo.
@@ -458,9 +463,29 @@ var _ControlDialPlanCloneNeedsRegeneration = ControlDialPlan(struct {
 	Candidates []ControlIPCandidate
 }{})
 
+// Clone makes a deep copy of Location.
+// The result aliases no memory with the original.
+func (src *Location) Clone() *Location {
+	if src == nil {
+		return nil
+	}
+	dst := new(Location)
+	*dst = *src
+	return dst
+}
+
+// A compilation failure here means this code must be regenerated, with the command at the top of this file.
+var _LocationCloneNeedsRegeneration = Location(struct {
+	Country     string
+	CountryCode string
+	City        string
+	CityCode    string
+	Priority    int
+}{})
+
 // Clone duplicates src into dst and reports whether it succeeded.
 // To succeed, <src, dst> must be of types <*T, *T> or <*T, **T>,
-// where T is one of User,Node,Hostinfo,NetInfo,Login,DNSConfig,RegisterResponse,DERPRegion,DERPMap,DERPNode,SSHRule,SSHAction,SSHPrincipal,ControlDialPlan.
+// where T is one of User,Node,Hostinfo,NetInfo,Login,DNSConfig,RegisterResponse,DERPRegion,DERPMap,DERPNode,SSHRule,SSHAction,SSHPrincipal,ControlDialPlan,Location.
 func Clone(dst, src any) bool {
 	switch src := src.(type) {
 	case *User:
@@ -589,6 +614,15 @@ func Clone(dst, src any) bool {
 			*dst = src.Clone()
 			return true
 		}
+	case *Location:
+		switch dst := dst.(type) {
+		case *Location:
+			*dst = *src.Clone()
+			return true
+		case **Location:
+			*dst = src.Clone()
+			return true
+		}
 	}
 	return false
 }