Prohibit tabs in whitespace check

[LilithHafner]

In general, tabs do not appear in well-formatted Julia source code. This automates that check.

• Prohibit tabs in whitespace check
• replace tabs with spaces and fix indentation

Is a superset of and closes #48697

This should possibly also cover other languages, but I don't know what our style conventions are for those languages and they are presumably less important to cover with this check.

This Does Not mean Julia code with tabs will error/warn/etc. It only effects the style enforcement of source code in this repo.

[LilithHafner]

bump

[StefanKarpinski]

I like this, in fact, so much so that I decided to purge tabs from other kinds of files as well. The code in src/support and src/flisp seems to consistently use tabs rather than spaces and rather than introduce a bunch of noise changing those files, I just excluded them from the check. We can skip whitespace-changing commits when generating blame, but I'm not sure if @JeffBezanson wants me changing all his C code from tabs to spaces. That code is very low churn anyway.

When this gets merged, it would be good to keep at least two commits: one that changes the whitespace and one that changes the check script. We want these separate so the whitespace one can be ignored in blame history. The order of the first two commits should be reversed, however, since the tests will fail after the first commit without the second one.

[KristofferC]

Rebased

[StefanKarpinski]

This looks good to me at this point. Should not be squashed—we want to keep both commits separate!

[StefanKarpinski]

@KristofferC, do you want to add the whitespace fix commit to the blameless file?

[KristofferC]

#49638