format bit flags as set

This changes to format output from:

    MyFlagType{ .first_bit = true, second_bit = false, _reserved_bit_0 = false, _reserved_bit_1 = false }

to the following:

    MyFlagType{ first_bit }

That is, we only show bits which are `true`.

generator/vulkan/render.zig

@@ -49,6 +49,7 @@ const preamble =
     \\        pub fn contains(lhs: FlagsType, rhs: FlagsType) bool {
     \\            return toInt(intersect(lhs, rhs)) == toInt(rhs);
     \\        }
+++ bit_flag_format ++
     \\    };
     \\}
     \\pub fn makeApiVersion(variant: u3, major: u7, minor: u10, patch: u12) u32 {
@@ -69,6 +70,31 @@ const preamble =
     \\
 ;
 
+const bit_flag_format =
+    \\        pub fn format(
+    \\            self: @This(),
+    \\            comptime _: []const u8,
+    \\            _: std.fmt.FormatOptions,
+    \\            writer: anytype,
+    \\        ) !void {
+    \\            try writer.writeAll(@typeName(@This()) ++ "{");
+    \\            var first = true;
+    \\            inline for (comptime std.meta.fieldNames(@This())) |name| {
+    \\                if (name[0] == '_') continue;
+    \\                if (@field(self, name)) {
+    \\                    if (first) {
+    \\                        try writer.writeAll(" " ++ name);
+    \\                        first = false;
+    \\                    } else {
+    \\                        try writer.writeAll(", " ++ name);
+    \\                    }
+    \\                }
+    \\            }
+    \\            if (!first) try writer.writeAll(" ");
+    \\            try writer.writeAll("}");
+    \\        }
+;
+
 const builtin_types = std.ComptimeStringMap([]const u8, .{
     .{ "void", @typeName(void) },
     .{ "char", @typeName(u8) },
@@ -1060,6 +1086,7 @@ fn Renderer(comptime WriterType: type) type {
                 \\            }
                 \\            return true;
                 \\        }
+            ++ bit_flag_format ++
                 \\    };
                 \\}
                 \\