breaking: Add positional, precision and width support to std.fmt

This removes the odd width and precision specifiers found and replacing
them with the more consistent api described in #1358.

Take the following example:

    {1:5.9}

This refers to the first argument (0-indexed) in the argument list. It
will be printed with a minimum width of 5 and will have a precision of 9
(if applicable).

Not all types correctly use these parameters just yet. There are still
some missing gaps to fill in. Fill characters and alignment have yet to
be implemented.

src-self-hosted/dep_tokenizer.zig

@@ -999,7 +999,7 @@ fn printCharValues(out: var, bytes: []const u8) !void {
 
 fn printUnderstandableChar(out: var, char: u8) !void {
     if (!std.ascii.isPrint(char) or char == ' ') {
-        std.fmt.format(out.context, anyerror, out.output, "\\x{X2}", char) catch {};
+        std.fmt.format(out.context, anyerror, out.output, "\\x{X:2}", char) catch {};
     } else {
         try out.write("'");
         try out.write([_]u8{printable_char_tab[char]});

std/math/big/int.zig

@@ -519,6 +519,7 @@ pub const Int = struct {
     pub fn format(
         self: Int,
         comptime fmt: []const u8,
+        comptime options: std.fmt.FormatOptions,
         context: var,
         comptime FmtError: type,
         output: fn (@typeOf(context), []const u8) FmtError!void,

std/special/build_runner.zig

@@ -170,7 +170,7 @@ fn usage(builder: *Builder, already_ran_build: bool, out_stream: var) !void {
 
     const allocator = builder.allocator;
     for (builder.top_level_steps.toSliceConst()) |top_level_step| {
-        try out_stream.print("  {s22} {}\n", top_level_step.step.name, top_level_step.description);
+        try out_stream.print("  {s:22} {}\n", top_level_step.step.name, top_level_step.description);
     }
 
     try out_stream.write(
@@ -191,7 +191,7 @@ fn usage(builder: *Builder, already_ran_build: bool, out_stream: var) !void {
         for (builder.available_options_list.toSliceConst()) |option| {
             const name = try fmt.allocPrint(allocator, "  -D{}=[{}]", option.name, Builder.typeIdName(option.type_id));
             defer allocator.free(name);
-            try out_stream.print("{s24} {}\n", name, option.description);
+            try out_stream.print("{s:24} {}\n", name, option.description);
         }
     }
 

test/compare_output.zig

@@ -122,7 +122,7 @@ pub fn addCases(cases: *tests.CompareOutputContext) void {
         \\
         \\pub fn main() void {
         \\    const stdout = &(io.getStdOut() catch unreachable).outStream().stream;
-        \\    stdout.print("Hello, world!\n{d4} {x3} {c}\n", u32(12), u16(0x12), u8('a')) catch unreachable;
+        \\    stdout.print("Hello, world!\n{d:4} {x:3} {c}\n", u32(12), u16(0x12), u8('a')) catch unreachable;
         \\}
     , "Hello, world!\n0012 012 a\n");