Apply API review fixes for MTROTAHeaderParser.

[bzbarsky-apple]

This is a re-landing of PR #22611 but with changes made for backwards compat.

• Move the parsing method to MTROTAHeader.
• Rename the file to MTROTAHeader.h
• Add documentation.

[github-actions]

PR #23479: Size comparison from 548da8b to 42fa20e

Increases (2 builds for bl602, bl702)

platform	target	config	section	548da8b	42fa20e	change	% change
bl602	lighting-app	bl602	(read/write)	1390790	1390798	8	0.0
			.text	1070024	1070026	2	0.0
bl702	lighting-app	bl702	.debug_info	38070211	38070212	1	0.0
			.text	957996	957998	2	0.0

Decreases (1 build for bl602)

platform	target	config	section	548da8b	42fa20e	change	% change
bl602	lighting-app	bl602+rpc	.text	1101630	1101628	-2	-0.0

Full report (7 builds for bl602, bl702, k32w)

platform	target	config	section	548da8b	42fa20e	change	% change
bl602	lighting-app	bl602	(read/write)	1390790	1390798	8	0.0
			.bss	90745	90745	0	0.0
			.data	9936	9936	0	0.0
			.text	1070024	1070026	2	0.0
		bl602+rpc	(read/write)	1436254	1436254	0	0.0
			.bss	98177	98177	0	0.0
			.data	10320	10320	0	0.0
			.text	1101630	1101628	-2	-0.0
bl702	lighting-app	bl702		0	0	0	0.0
			(read only)	3262	3262	0	0.0
			(read/write)	1189595	1189595	0	0.0
			.bleromro	6296	6296	0	0.0
			.bleromrw	124	124	0	0.0
			.boot2	688	688	0	0.0
			.bss	67134	67134	0	0.0
			.bss_psram	29696	29696	0	0.0
			.comment	48	48	0	0.0
			.data	4280	4280	0	0.0
			.debug_abbrev	1513310	1513310	0	0.0
			.debug_aranges	132072	132072	0	0.0
			.debug_frame	484468	484468	0	0.0
			.debug_info	38070211	38070212	1	0.0
			.debug_line	5263909	5263909	0	0.0
			.debug_loc	3366772	3366772	0	0.0
			.debug_ranges	358128	358128	0	0.0
			.debug_str	3451743	3451743	0	0.0
			.hbn	509	509	0	0.0
			.hbn_noinit	260	260	0	0.0
			.init	342	342	0	0.0
			.init_array	144	144	0	0.0
			.psram	0	0	0	0.0
			.riscv.attributes	47	47	0	0.0
			.rodata	116680	116680	0	0.0
			.rsvd	3188	3188	0	0.0
			.shstrtab	293	293	0	0.0
			.stack	2048	2048	0	0.0
			.strtab	566021	566021	0	0.0
			.symtab	172000	172000	0	0.0
			.tcm_data	36	36	0	0.0
			.tcmcode	3262	3262	0	0.0
			.text	957996	957998	2	0.0
		bl702+rpc		0	0	0	0.0
			(read only)	3262	3262	0	0.0
			(read/write)	1285539	1285539	0	0.0
			.bleromro	6296	6296	0	0.0
			.bleromrw	124	124	0	0.0
			.boot2	688	688	0	0.0
			.bss	75166	75166	0	0.0
			.bss_psram	29936	29936	0	0.0
			.comment	48	48	0	0.0
			.data	4816	4816	0	0.0
			.debug_abbrev	1650724	1650724	0	0.0
			.debug_aranges	139576	139576	0	0.0
			.debug_frame	509840	509840	0	0.0
			.debug_info	41986318	41986318	0	0.0
			.debug_line	5639643	5639643	0	0.0
			.debug_loc	3559599	3559599	0	0.0
			.debug_ranges	380928	380928	0	0.0
			.debug_str	3847871	3847871	0	0.0
			.hbn	509	509	0	0.0
			.hbn_noinit	260	260	0	0.0
			.init	342	342	0	0.0
			.init_array	160	160	0	0.0
			.psram	0	0	0	0.0
			.riscv.attributes	47	47	0	0.0
			.rodata	130088	130088	0	0.0
			.rsvd	3188	3188	0	0.0
			.shstrtab	293	293	0	0.0
			.stack	2048	2048	0	0.0
			.strtab	625194	625194	0	0.0
			.symtab	189808	189808	0	0.0
			.tcm_data	36	36	0	0.0
			.tcmcode	3262	3262	0	0.0
			.text	1031702	1031702	0	0.0
k32w	contact	k32w0+release	(read/write)	661676	661676	0	0.0
			.bss	77040	77040	0	0.0
			.data	2104	2104	0	0.0
			.text	563420	563420	0	0.0
	light	k32w0+release	(read/write)	672008	672008	0	0.0
			.bss	74840	74840	0	0.0
			.data	2060	2060	0	0.0
			.text	592380	592380	0	0.0
	lock	k32w0+release	(read/write)	633484	633484	0	0.0
			.bss	75600	75600	0	0.0
			.data	2080	2080	0	0.0
			.text	553076	553076	0	0.0

[bzbarsky-apple]

Fast-tracking platform-specific fix with platform owner review.