Instead of runtime null, duplicate, and capacity checks in
register_component_, make the method unreachable from outside
codegen by removing the public template wrapper and granting
friend access to the codegen-generated ::setup() function.
Since ESPHOME_COMPONENT_COUNT is set to exactly
len(CORE.component_ids) at codegen time, the StaticVector is
always correctly sized and the runtime capacity check cannot
trigger from codegen. External components that bypassed codegen
to call App.register_component() directly will now get a
compile error, forcing them to properly declare their components
in their config schema.
Co-Authored-By: J. Nick Koston <nick@koston.org>
