resolved: move DNS RR/key/answer/question/packet tools to shared/

We want to reuse these generic DNS concepts in resolved hook
implementations, hence move them to shared code.

(This also enables us to immediately remove som SVCB record handling
duplicate definitions.)

No real code changes, just some moving around of things.

src/shared/shared-forward.h

@@ -18,8 +18,10 @@ typedef enum BusPrintPropertyFlags BusPrintPropertyFlags;
 typedef enum BusTransport BusTransport;
 typedef enum CatFlags CatFlags;
 typedef enum CertificateSourceType CertificateSourceType;
+typedef enum DnsAnswerFlags DnsAnswerFlags;
 typedef enum DnsCacheMode DnsCacheMode;
 typedef enum DnsOverTlsMode DnsOverTlsMode;
+typedef enum DnsProtocol DnsProtocol;
 typedef enum DnssecMode DnssecMode;
 typedef enum Fido2EnrollFlags Fido2EnrollFlags;
 typedef enum KeySourceType KeySourceType;
@@ -50,6 +52,13 @@ typedef struct Condition Condition;
 typedef struct ConfigSection ConfigSection;
 typedef struct ConfigTableItem ConfigTableItem;
 typedef struct CPUSet CPUSet;
+typedef struct DnsAnswer DnsAnswer;
+typedef struct DnsPacket DnsPacket;
+typedef struct DnsQuestion DnsQuestion;
+typedef struct DnsResourceKey DnsResourceKey;
+typedef struct DnsResourceRecord DnsResourceRecord;
+typedef struct DnsSvcParam DnsSvcParam;
+typedef struct DnsTxtItem DnsTxtItem;
 typedef struct FDSet FDSet;
 typedef struct Fido2HmacSalt Fido2HmacSalt;
 typedef struct GroupRecord GroupRecord;