ipn/ipnlocal: use policyclient.Client always, stop using global syspolicy funcs

Step 4 of N. See earlier commits in the series (via the issue) for the
plan.

This adds the missing methods to policyclient.Client and then uses it
everywhere in ipn/ipnlocal and locks it in with a new dep test.

Still plenty of users of the global syspolicy elsewhere in the tree,
but this is a lot of them.

Updates #16998
Updates #12614

Change-Id: I25b136539ae1eedbcba80124de842970db0ca314
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

tsd/syspolicy_on.go

@@ -6,9 +6,12 @@
 package tsd
 
 import (
+	"time"
+
 	"tailscale.com/util/syspolicy"
 	"tailscale.com/util/syspolicy/pkey"
 	"tailscale.com/util/syspolicy/policyclient"
+	"tailscale.com/util/syspolicy/ptype"
 )
 
 func getPolicyClient() policyclient.Client { return globalSyspolicy{} }
@@ -36,6 +39,26 @@ func (globalSyspolicy) SetDebugLoggingEnabled(enabled bool) {
 	syspolicy.SetDebugLoggingEnabled(enabled)
 }
 
+func (globalSyspolicy) GetUint64(key pkey.Key, defaultValue uint64) (uint64, error) {
+	return syspolicy.GetUint64(key, defaultValue)
+}
+
+func (globalSyspolicy) GetDuration(name pkey.Key, defaultValue time.Duration) (time.Duration, error) {
+	return syspolicy.GetDuration(name, defaultValue)
+}
+
+func (globalSyspolicy) GetPreferenceOption(name pkey.Key) (ptype.PreferenceOption, error) {
+	return syspolicy.GetPreferenceOption(name)
+}
+
+func (globalSyspolicy) GetVisibility(name pkey.Key) (ptype.Visibility, error) {
+	return syspolicy.GetVisibility(name)
+}
+
+func (globalSyspolicy) HasAnyOf(keys ...pkey.Key) (bool, error) {
+	return syspolicy.HasAnyOf(keys...)
+}
+
 func (globalSyspolicy) RegisterChangeCallback(cb func(policyclient.PolicyChange)) (unregister func(), err error) {
 	return syspolicy.RegisterChangeCallback(cb)
 }