Make sure DnssdServer does not dereference a dangling fabric table.

[bzbarsky-apple]

We could end up not calling StopServer if the last release of a system state was a direct release on the state itself, not a call to ReleaseSystemState.

To fix this, move the DnssdServer::StopServer bits into the actual system state shutdown, where we know whether we are destroying the fabric table that DnssdServer uses and can clean up appropriately.

[github-actions]

PR #26354: Size comparison from 79bedcf to c5f5a8d

Increases (1 build for cc32xx)

platform	target	config	section	79bedcf	c5f5a8d	change	% change
cc32xx	lock	CC3235SF_LAUNCHXL	.debug_info	19522304	19522306	2	0.0
			.debug_line	2666090	2666098	8	0.0

Full report (1 build for cc32xx)

platform	target	config	section	79bedcf	c5f5a8d	change	% change
cc32xx	lock	CC3235SF_LAUNCHXL		0	0	0	0.0
			(read only)	604722	604722	0	0.0
			(read/write)	204156	204156	0	0.0
			.ARM.attributes	44	44	0	0.0
			.ARM.exidx	8	8	0	0.0
			.bss	197568	197568	0	0.0
			.comment	206	206	0	0.0
			.data	1468	1468	0	0.0
			.debug_abbrev	956987	956987	0	0.0
			.debug_aranges	101104	101104	0	0.0
			.debug_frame	341416	341416	0	0.0
			.debug_info	19522304	19522306	2	0.0
			.debug_line	2666090	2666098	8	0.0
			.debug_line_str	513	513	0	0.0
			.debug_loc	33340	33340	0	0.0
			.debug_loclists	1488715	1488715	0	0.0
			.debug_ranges	4984	4984	0	0.0
			.debug_rnglists	94279	94279	0	0.0
			.debug_str	3100491	3100491	0	0.0
			.ramVecs	780	780	0	0.0
			.resetVecs	64	64	0	0.0
			.rodata	104298	104298	0	0.0
			.shstrtab	265	265	0	0.0
			.stack	2048	2048	0	0.0
			.strtab	482872	482872	0	0.0
			.symtab	287120	287120	0	0.0
			.text	498300	498300	0	0.0