What about a quick loop instead of the regex (plus tab support):

let indent = '';
for (const char of text) {
    if (char === ' ' || char === '\u0009') {
        indent += char;
    } else {
        break;
    }
}

I personally like RegExps, but happy to change it to whatever you prefer (or even keep the original version).
I just happened to go through the files trying to fix something else and made some changes that made sense to me (and hopefully to others).

I'm partial to the more self explanatory nature of the loop above then the other two options. And it definitely performs better than the first.

To each his own 😛
Happy to change it to a for loop.

Adding this to the actual template index.html may make sense since it applies to a standard web applications as well. Thoughts?

True. I guess this was added as poart of @angular/pwa, because good PWA practices include having fallback content for when JS is disabled, but this is indeed useful for non-PWA apps as well.
Should Imove it to index.html?

I think it eventually should but probably should be left to a separate PR. However, the addition here would need to stay either way to support projects that didn't get created with the new index.html. The code here should be augment now though to check if the noscriptelement is already present and only add if not. Since someone could have added the element manually as well.

Actually, I just realized that a proper solution should also check whether link[rel="manifest"] and meta[name="theme-color"] already exist as well. Since this PR is only refactoring that part of the code (no behavior changes), I'd rather leave the checks for another PR.

Good point and works for me.