AK: Implement Stream::format(fmtstr, args...)

Based on `out()` and `vout()` from AK/Format.h. As opposed to those,
this propagates errors.

As `Core::File` extends `AK::Stream`, this allows formatted
printing directly on `Core::File`s.

AK/Stream.cpp

@@ -8,6 +8,7 @@
 #include <AK/ByteBuffer.h>
 #include <AK/Format.h>
 #include <AK/Stream.h>
+#include <AK/StringBuilder.h>
 
 namespace AK {
 
@@ -97,6 +98,16 @@ ErrorOr<void> Stream::write_until_depleted(ReadonlyBytes buffer)
     return {};
 }
 
+ErrorOr<void> Stream::format_impl(StringView fmtstr, TypeErasedFormatParams& parameters)
+{
+    StringBuilder builder;
+    TRY(vformat(builder, fmtstr, parameters));
+
+    auto const string = builder.string_view();
+    TRY(write_until_depleted(string.bytes()));
+    return {};
+}
+
 ErrorOr<size_t> SeekableStream::tell() const
 {
     // Seek with 0 and SEEK_CUR does not modify anything despite the const_cast,

AK/Stream.h

@@ -8,6 +8,7 @@
 #pragma once
 
 #include <AK/Error.h>
+#include <AK/Format.h>
 #include <AK/Forward.h>
 #include <AK/Traits.h>
 
@@ -76,6 +77,16 @@ public:
         return write_until_depleted({ &value, sizeof(value) });
     }
 
+    virtual ErrorOr<void> format_impl(StringView, TypeErasedFormatParams&);
+
+    template<typename... Parameters>
+    ErrorOr<void> format(CheckedFormatString<Parameters...>&& fmtstr, Parameters const&... parameters)
+    {
+        VariadicFormatParams<AllowDebugOnlyFormatters::No, Parameters...> variadic_format_params { parameters... };
+        TRY(format_impl(fmtstr.view(), variadic_format_params));
+        return {};
+    }
+
     /// Returns whether the stream has reached the end of file. For sockets,
     /// this most likely means that the protocol has disconnected (in the case
     /// of TCP). For seekable streams, this means the end of the file. Note that