Swap \; for \, in LatexifyExt and matching tests

[Ickaser]

As briefly discussed in #795 (comment), it's marginally more appealing to use a thin space (\,) than the wider space (\;) between the number and unit of a quantity. This is also the default behavior in LaTeX's siunitx.

This PR makes that change (fortunately a two-character change), as well as updating the corresponding tests.
Current master:

This PR:

The aspect which could depend on taste is that I also removed the spacing between an array and its unit, which seems to visually match the regular quantity spacing.

For arrays, options are:
With \, (third option this PR): (\begin{equation} \left[ \begin{array}{c} 1 \\ 2 \\ 3 \\ \end{array} \right]\,\mathrm{m} \end{equation})

With \; (current master):

With no extra spacing at all (this PR former version of this PR): (\begin{equation} \left[ \begin{array}{c} 1 \\ 2 \\ 3 \\ \end{array} \right]\mathrm{m} \end{equation})

The one caveat I see to removing the space between array and unit is that, formally, the space should be left out when the unit is degrees, and so this puts other units at the same separation as degrees (instead of having an extra space).

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[giordano]

Did you push cf9ad06 to the wrong branch?

[Ickaser]

Did you push cf9ad06 to the wrong branch?

Yep, reverting that here

[sostock]

For consistency, I would go with the third option, but it’s not a strong preference.

[Ickaser]

Consistency is good, I'll put the \, back in. @gustaphe any thoughts on space between array and unit before this merges?

[gustaphe]

No opinion, array times unit looks awkward either way, and when they are not side by side I doubt anyone will register the difference :D

I like the PR in general.