[dsnsd-server] support handling of "A record" queries

[abtink]

This commit adds support for responding to "A record" queries in the DNS-SD server and discovery proxy.

If the query matches a host registered with the SRP server, the host's IPv6 addresses are returned in the Additional Data section of the response. If the query is resolved by the proxy, the otPlatDnssd APIs are used to start/stop IPv4 address resolvers for the hostname on the infrastructure network.

The test_dnssd_discovery_proxy unit test is updated to validate the new functionality.

[size-report]

Size Report of OpenThread

Merging #10364 into main(32f462f).

name	branch	text	data	bss	total
ot-cli-ftd	main	466568	856	66332	533756
	#10364	466568	856	66332	533756
	+/-	0	0	0	0
ot-ncp-ftd	main	435516	760	61544	497820
	#10364	435516	760	61544	497820
	+/-	0	0	0	0
libopenthread-ftd.a	main	235735	95	40278	276108
	#10364	235735	95	40278	276108
	+/-	0	0	0	0
libopenthread-cli-ftd.a	main	57589	0	8075	65664
	#10364	57589	0	8075	65664
	+/-	0	0	0	0
libopenthread-ncp-ftd.a	main	31947	0	5916	37863
	#10364	31947	0	5916	37863
	+/-	0	0	0	0
ot-cli-mtd	main	364552	760	51204	416516
	#10364	364552	760	51204	416516
	+/-	0	0	0	0
ot-ncp-mtd	main	347140	760	46432	394332
	#10364	347140	760	46432	394332
	+/-	0	0	0	0
libopenthread-mtd.a	main	157934	0	25166	183100
	#10364	157934	0	25166	183100
	+/-	0	0	0	0
libopenthread-cli-mtd.a	main	39812	0	8059	47871
	#10364	39812	0	8059	47871
	+/-	0	0	0	0
libopenthread-ncp-mtd.a	main	24827	0	5916	30743
	#10364	24827	0	5916	30743
	+/-	0	0	0	0
ot-cli-ftd-br	main	550336	864	131172	682372
	#10364	550528	864	131172	682564
	+/-	+192	0	0	+192
libopenthread-ftd-br.a	main	323969	100	105094	429163
	#10364	324159	100	105094	429353
	+/-	+190	0	0	+190
libopenthread-cli-ftd-br.a	main	71450	0	8099	79549
	#10364	71450	0	8099	79549
	+/-	0	0	0	0
ot-rcp	main	62280	564	20604	83448
	#10364	62280	564	20604	83448
	+/-	0	0	0	0
libopenthread-rcp.a	main	9554	0	5052	14606
	#10364	9554	0	5052	14606
	+/-	0	0	0	0
libopenthread-radio.a	main	19042	0	214	19256
	#10364	19042	0	214	19256
	+/-	0	0	0	0