std.Build.Step.Options: handle std.log.Level and std.log.ScopeLevel

[dweiller]

This change adds support for std.log.Level and std.log.ScopeLevel to std.Build.Step.Options, similar to the existing support for std.SemanticVersion. Makes it more straightforward to provide build options for configuring logging by removing the need to use @enumFromInt and @intFromEnum (or some other serialisation scheme).

With this change it becomes possible to do this:

// build.zig
pub fn build(b: *std.Build) void {
    const options = b.addOptions();
    const log_level: std.log.Level = b.option(std.log.Level, "log-level", "Most verbose log level") orelse .info;
    options.addOption(std.log.Level, "log_level", log_level);

    const root_module = b.createModule(.{
        .root_source_file = b.path("src/main.zig"),
    };

    root_module.addOptions("build_options", options);

    const exe = b.addExecutable(.{
        .name = "prog",
        .root_module = root_module,
    });
}

// src/main.zig

const std_options: std.Options = .{
    .log_level = @import("build_options").log_level,
};

Without this change, you would need to do:

     const log_level: std.log.Level = b.option(std.log.Level, "log-level", "Most verbose log level") orelse .info;
-    options.addOption(std.log.Level, "log_level", log_level);
+    options.addOption(u2, "log_level", @intFromEnum(log_level));

 const std_options: std.Options = .{
-    .log_level = @import("build_options").log_level,
+    .log_level = @enumFromInt(@import("build_options").log_level),
 };

which isn't too bad, but it gets more annoying when wanting to use std.log.ScopeLevels.