LibCore: Add Stream::read_all()

Author: https://github.com/msvisser
Commit: 68772463cb
Pull-request: https://github.com/SerenityOS/serenity/pull/13384
Reviewed-by: https://github.com/Lubrsi
Reviewed-by: https://github.com/alimpfard
Reviewed-by: https://github.com/creator1creeper1
Reviewed-by: https://github.com/kleinesfilmroellchen ✅

Userland/Libraries/LibCore/Stream.h

@@ -37,6 +37,7 @@ public:
     /// Tries to fill the entire buffer through reading. Returns whether the
     /// buffer was filled without an error.
     virtual bool read_or_error(Bytes);
+    ErrorOr<ByteBuffer> read_all();
 
     virtual bool is_writable() const { return false; }
     /// Tries to write the entire contents of the buffer. It is possible for