ConfigHeader does not automatically register a generated FileSource as a step dependency

[distractedlambda]

Zig Version

0.11.0-dev.3803+7ad104227

Steps to Reproduce and Observed Behavior

The cmake and autoconf styles of ConfigHeader take a FileSource for the input header, and do indeed work with generated files, but they do not automatically add a dependency on the generation step.

Expected Behavior

I would expect the dependency to be added automatically, as this is almost certainly the user's intention, and is already done elsewhere in the build script API.

[matu3ba]

Polite ping @Jan200101, if you want to poke this and/or #16203. If you prefer not to be pinged, let me know.

[Jan200101]

I'm fine with being pinged.

Already PR'd a fix for 16203 but am unsure how the requested behavior should look like (plus I think this is a feature request / proposal not a bug report).

Would an example of the requested behavior be passing a header through multiple ConfigHeader's and having the implicit dependencies established?

e.g.

const std = @import("std");

pub fn build(b: *std.Build) void {
    // first we pass it through cmake
    const cmake_config = b.addConfigHeader(.{ .style = .{ .cmake = .{ .path = "config.h.in" } } }, .{});

    // then through autoconf
    const autoconf_confing = b.addConfigHeader(.{ .style = .{ .autoconf = .{ .path = cmake_config.getFileSource() } } }, .{});

    const install_autoconf_config = b.addInstallFile(autoconf_confing.getFileSource(), "config-autoconf.h");
    b.getInstallStep().dependOn(&install_autoconf_config.step);
}