Consider integrating `zig fmt` into the build

[alexrp]

Something like:

• On Build, run zig fmt --check if EnforceCodeStyleInBuild is set.
• Add a Format target that actually formats source files (i.e. just zig fmt <sources>).

[alexrp]

• A FormatOnBuild property would also be useful.
• The Format target should always just do zig fmt.
• If EnforceCodeStyleInBuild is set, run zig fmt --check before building.
• If FormatOnBuild is set, run zig fmt before building (ignoring EnforceCodeStyleInBuild).