Split code into modules

This is a massive commit that restructures the code into modules:

db/
    All functions related to modifying the Database

types/
    All type definitions and methods that can be exclusivly used on
    these types without dependencies

policy/
    All Policy related code, now without dependencies on the Database.

policy/matcher/
    Dedicated code to match machines in a list of FilterRules

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

hscontrol/policy/matcher/matcher.go

@@ -0,0 +1,61 @@
+package matcher
+
+import (
+	"net/netip"
+
+	"github.com/juanfont/headscale/hscontrol/util"
+	"go4.org/netipx"
+	"tailscale.com/tailcfg"
+)
+
+type Match struct {
+	Srcs  *netipx.IPSet
+	Dests *netipx.IPSet
+}
+
+func MatchFromFilterRule(rule tailcfg.FilterRule) Match {
+	srcs := new(netipx.IPSetBuilder)
+	dests := new(netipx.IPSetBuilder)
+
+	for _, srcIP := range rule.SrcIPs {
+		set, _ := util.ParseIPSet(srcIP, nil)
+
+		srcs.AddSet(set)
+	}
+
+	for _, dest := range rule.DstPorts {
+		set, _ := util.ParseIPSet(dest.IP, nil)
+
+		dests.AddSet(set)
+	}
+
+	srcsSet, _ := srcs.IPSet()
+	destsSet, _ := dests.IPSet()
+
+	match := Match{
+		Srcs:  srcsSet,
+		Dests: destsSet,
+	}
+
+	return match
+}
+
+func (m *Match) SrcsContainsIPs(ips []netip.Addr) bool {
+	for _, ip := range ips {
+		if m.Srcs.Contains(ip) {
+			return true
+		}
+	}
+
+	return false
+}
+
+func (m *Match) DestsContainsIP(ips []netip.Addr) bool {
+	for _, ip := range ips {
+		if m.Dests.Contains(ip) {
+			return true
+		}
+	}
+
+	return false
+}