Add StaticVector for NotificationManager

[Riksu9000]

Apart from renaming some public functions to reduce ambiguity, this does not change the behavior of the class IndexOf won't return an invalid index anymore, so there are minor differences in (unused) edge cases Reverted so Get() can return an empty notification if the id is invalid.. Using a vector-like class makes it so the newest element has the highest index, whereas before At(0) was the newest entry. A new function was added to get the position of the notification where 0 is the newest one, to imitate the behavior of the old previously public IndexOf() function.

[github-actions[bot]]

Build size and comparison to main:	Section	Size	Difference
text	406244B	-244B
data	940B	0B
bss	53552B	-8B