Replace hard-coded values for spacing with variables specified on _spacing.pcss

[luixxiul]

Your use case

What would you like to do?

Replace hard-coded values for spacing with variables specified on _spacing.pcss.

Why would you like to do it?

Because the style guide suggests you to use a variable for a property related to spacing. It should also help us to maintain the themes' consistency.

How would you like to achieve it?

Search padding and margin values and replace them.

Have you considered any alternatives?

No response

Additional context

This should be conducted along with matrix-org/matrix-react-sdk#10552 for #21656.

[NSV1991]

@luixxiul I like to work on this enhancement.
What is the intended scope for the changes for this enhancement?
I mean which module we should target first?

[richvdh]

So, I discussed this with the rest of the team, with conclusions as follows:

Let's not do this: it seems like a lot of work for both authors and reviewers, for no tangible benefit.

There is debate over whether the current $spacing- variables offer any value at all (see matrix-org/matrix-react-sdk#10686), but even if we do want to use them going forward, we don't think a wholesale replacement of existing values offers any value at all.

In the longer term, we'd like to use components based on our "Compound" design system, which will use semantic variables rather than hardcoding particular px values, but that requires design input and updating legacy components is not a priority for the design team.