Remove some unnecessary nullable annotations.

[bzbarsky-apple]

Just need to initialize things in the initializer list instead of
default-constructing them as nil and then initializing them.

Problem

See above.

Change overview

See above.

Testing

No behavior changes, still passes clang-tidy lints.

[github-actions]

PR #17799: Size comparison from 99988e5 to 632e313

Full report (23 builds for cc13x2_26x2, cyw30739, efr32, esp32, k32w, linux, mbed, nrfconnect, p6, telink)

platform	target	config	section	99988e5	632e313	change	% change
cc13x2_26x2	all-clusters-app	LP_CC2652R7	(read only)	688327	688327	0	0.0
			(read/write)	163712	163712	0	0.0
			.bss	75020	75020	0	0.0
			.data	3396	3396	0	0.0
			.rodata	101583	101583	0	0.0
			.text	586264	586264	0	0.0
	lock-ftd	LP_CC2652R7	(read only)	689047	689047	0	0.0
			(read/write)	154304	154304	0	0.0
			.bss	73388	73388	0	0.0
			.data	3220	3220	0	0.0
			.rodata	103247	103247	0	0.0
			.text	585316	585316	0	0.0
	lock-mtd	LP_CC2652R7	(read only)	637791	637791	0	0.0
			(read/write)	146188	146188	0	0.0
			.bss	69108	69108	0	0.0
			.data	3220	3220	0	0.0
			.rodata	103127	103127	0	0.0
			.text	534172	534172	0	0.0
	pump-app	LP_CC2652R7	(read only)	661891	661891	0	0.0
			(read/write)	182660	182660	0	0.0
			.bss	73564	73564	0	0.0
			.data	3252	3252	0	0.0
			.rodata	80443	80443	0	0.0
			.text	580968	580968	0	0.0
	pump-controller-app	LP_CC2652R7	(read only)	654787	654787	0	0.0
			(read/write)	189556	189556	0	0.0
			.bss	73612	73612	0	0.0
			.data	3216	3216	0	0.0
			.rodata	83467	83467	0	0.0
			.text	570840	570840	0	0.0
cyw30739	light	cyw930739m2evb_01	(read/write)	626890	626890	0	0.0
			.app_xip_area	529768	529768	0	0.0
			.bss	79780	79780	0	0.0
			.data	692	692	0	0.0
			.rodata	0	0	0	0.0
			.text	0	0	0	0.0
	lock	cyw930739m2evb_01	(read/write)	621434	621434	0	0.0
			.app_xip_area	525784	525784	0	0.0
			.bss	78340	78340	0	0.0
			.data	656	656	0	0.0
			.rodata	0	0	0	0.0
			.text	0	0	0	0.0
	ota-requestor-no-progress-logging	cyw930739m2evb_01	(read/write)	574262	574262	0	0.0
			.app_xip_area	468968	468968	0	0.0
			.bss	87688	87688	0	0.0
			.data	568	568	0	0.0
			.rodata	0	0	0	0.0
			.text	112	112	0	0.0
efr32	lighting-app	BRD4161A	(read only)	907908	907908	0	0.0
			(read/write)	134908	134908	0	0.0
			.bss	132864	132864	0	0.0
			.data	2044	2044	0	0.0
			.text	907900	907900	0	0.0
		BRD4161A+rpc	(read only)	942308	942308	0	0.0
			(read/write)	151592	151592	0	0.0
			.bss	149344	149344	0	0.0
			.data	2248	2248	0	0.0
			.text	942300	942300	0	0.0
	window-app	BRD4161A	(read only)	845276	845276	0	0.0
			(read/write)	132996	132996	0	0.0
			.bss	131040	131040	0	0.0
			.data	1956	1956	0	0.0
			.text	845268	845268	0	0.0
esp32	all-clusters-app	c3devkit	(read only)	999528	999528	0	0.0
			(read/write)	1473690	1473690	0	0.0
			.dram0.bss	68176	68176	0	0.0
			.dram0.data	14428	14428	0	0.0
			.flash.rodata	206640	206640	0	0.0
			.flash.text	999528	999528	0	0.0
			.iram0.text	62020	62020	0	0.0
		m5stack	(read only)	1053803	1053803	0	0.0
			(read/write)	475688	475688	0	0.0
			.dram0.bss	73696	73696	0	0.0
			.dram0.data	34168	34168	0	0.0
			.flash.rodata	235988	235988	0	0.0
			.flash.text	1048419	1048419	0	0.0
			.iram0.text	123107	123107	0	0.0
k32w	light	k32w061+release	(read/write)	688824	688824	0	0.0
			.bss	81112	81112	0	0.0
			.data	2000	2000	0	0.0
			.text	599912	599912	0	0.0
	lock	k32w061+release	(read/write)	729684	729684	0	0.0
			.bss	81520	81520	0	0.0
			.data	1960	1960	0	0.0
			.text	640404	640404	0	0.0
linux	chip-tool-no-interactive-ipv6only	arm64	(read only)	8222460	8222460	0	0.0
			(read/write)	537745	537745	0	0.0
			.bss	40897	40897	0	0.0
			.data	1192	1192	0	0.0
			.data.rel.ro	477752	477752	0	0.0
			.dynamic	560	560	0	0.0
			.got	14080	14080	0	0.0
			.init	24	24	0	0.0
			.init_array	184	184	0	0.0
			.rodata	419452	419452	0	0.0
			.text	6589060	6589060	0	0.0
	thermostat-no-ble	arm64	(read only)	2368540	2368540	0	0.0
			(read/write)	174337	174337	0	0.0
			.bss	86097	86097	0	0.0
			.data	1488	1488	0	0.0
			.data.rel.ro	78984	78984	0	0.0
			.dynamic	560	560	0	0.0
			.got	4744	4744	0	0.0
			.init	24	24	0	0.0
			.init_array	368	368	0	0.0
			.rodata	145532	145532	0	0.0
			.text	1993984	1993984	0	0.0
mbed	lock-app	CY8CPROTO_062_4343W+release	(read only)	6224	6224	0	0.0
			(read/write)	2411772	2411772	0	0.0
			.bss	205660	205660	0	0.0
			.data	5848	5848	0	0.0
			.text	1374372	1374372	0	0.0
nrfconnect	all-clusters-app	nrf52840dk_nrf52840	(read/write)	1179487	1179487	0	0.0
			bss	141784	141784	0	0.0
			rodata	150272	150272	0	0.0
			text	808800	808800	0	0.0
p6	all-clusters-app	default	(read/write)	2527216	2527216	0	0.0
			.bss	139040	139040	0	0.0
			.data	2784	2784	0	0.0
			.text	1485480	1485480	0	0.0
	light-app	default	(read/write)	2418960	2418960	0	0.0
			.bss	132520	132520	0	0.0
			.data	2584	2584	0	0.0
			.text	1377224	1377224	0	0.0
	lock-app	default	(read/write)	2423136	2423136	0	0.0
			.bss	132320	132320	0	0.0
			.data	2544	2544	0	0.0
			.text	1381400	1381400	0	0.0
telink	lighting-app	tlsr9518adk80d	(read/write)	808144	808144	0	0.0
			bss	75216	75216	0	0.0
			noinit	40416	40416	0	0.0
			text	571886	571886	0	0.0