Use tabs (U+0009) for autoformatting indentation

[toastal]

The tab character is a more user-friendly & accessible option for indentation since users can configure the width for whatever their preference desires or impairment requires. Printing becomes simpler for indentation depth (where 1 \t = 1 level of indentation). As a bonus, the output size is smaller not filled with more separating spaces than is required.

According to the spec https://github.com/kdl-org/kdl/blob/main/SPEC.md#whitespace, U+0009 is considered “non-Newline white space” & is allowable.

At a minimum, it would be nice to to see tabs supported as an option, but this would make indention a more complicated input ADT of enum Indent { Tab, Space(u8) } to support tabs & configurable space depth.

See more arguments (be warned there is a lot of bike-shedding, however many legitimate concerns): prettier/prettier#7475