Devicetree formatting configuration

[nickcoutsos]

Relating to zmkfirmware/zmk#583.

Since switching from generating a new .keymap file on commit to editing the Devicetree code in an existing file, I've started applying some generic formatting rules to help with consistency. Some of these rules are pretty agreeable like "don't try to format the contents of integer cell arrays when they span multiple lines" (because this is how layer bindings are expressed and special formatting is applied here already as a core feature of this app), but I expect people to have lots of opinions about other ones.

Current experimental configuration:

1. indent -- the text to insert for each level of indentation such as the default four-space indent (" ") or a hard-tab ("\t"). Trusting you to not do something goofy and break your own keymap.
2. multilineIntegerCellsIndent -- how to handle indentation of values like layer bindings. This won't affect alignment of the binding cells relative to one another, but whether the common indentation should match the node's depth or if the indentation should be removed (this can help to avoid text wrapping for long-ish lines). Options here are:
   • "reindent": apply the level of indentation appropriate for the node's depth
   • "dedent": remove any indentation from these lines
   • "keep" (default): don't make any changes. Because this mainly applies to layer bindings which are already indented by the layout code this doesn't have much effect.

Example usage in zmk-config-corne-demo

Potential additional configuration:

• When writing out bindings for macros I logically group control bindings (e.g. &macro_tap and others) separately from others, and then for readability I split each "group" of integer cells onto its own line. This is all well and good for macros but this part of the formatter is agnostic of ZMK so it applies to any property with multiple integer cells values (e.g. foo = <1 2>, <3 4>; vs foo = <1 2 3 4>;). Maybe this could be refined with a rule about the overall length of the values.
• Along with the above, I'm formatting these on multiple lines like:

  foo = 
    <blah blah blah>,
    <blah blah blah>,
    <blah blah blah>;
  

  versus the examples in ZMK's macro documentation:

  foo
    = <blah blah blah>
    , <blah blah blah>
    ;
  

  I'm not a fan of the latter but given that its used in the ZMK documentation it's reasonable to expect it.
• When formatting layer bindings I right-align columns because I feel like the bind parameter is usually more important to compare than the behavior. There's no reason why this couldn't be left-aligned so it could be configurable... perhaps even a "justified" version where a behavior and its binding cells are spaced evenly to use the maximum width of that column.

I'd be very interested from hearing other thoughts on this.