Header: fix project update updates

[breville]

It was recently observed that the header's ScriptName component -- which contains the script name and sometimes the ProjectUpdatedAt component below that which shows text like "Saved 2 hours ago" -- was being cropped at its right edge.

While I wasn't able to get a firm local repro, I was able to simulate the suspected issue: the ProjectUpdatedAt component was having its content updated, but the parent ScriptName component didn't know that, so it didn't tell its parent HeaderMiddle component about the newly-desired width.

I'm not sure whether this was always an issue, or something new in a recent React update, but the fix is pretty simple: when the ProjectUpdatedAt component is updated, it informs its parent ScriptName, which then determines the width of the resulting content, and tells its parent HeaderMiddle, which can go about reallocating space appropriately.

The simulation of this issue simply put a timer inside ProjectUpdatedAt which rendered a random length string every second.

Before, we can see that HeaderMiddle isn't reallocating space:

header-projects-before-3.mov

After, we can see that HeaderMiddle reallocates spaces:

header-projects-after-3.mov

This counts as a follow-up to #34551.

[maddiedierker]

not blocking for this PR, but i have a general approach question: why are we using javascript to manage the navbar component/element widths rather than CSS?

[breville]

not blocking for this PR, but i have a general approach question: why are we using javascript to manage the navbar component/element widths rather than CSS?

#34551 goes into a lot of detail, but essentially JavaScript allows us to be a lot more expressive about the allocation of space depending on a variety of factors, as can be seen in the implementation of getWidths in HeaderMiddle. And it lets us do special things, like the most advanced piece of layout in that PR, in which LessonProgress has its content placed so that the current level bubble is always visible, and centered where possible, within the available space.