LibCore+Everywhere: Make Core::Stream::read() return Bytes

A mistake I've repeatedly made is along these lines:
```c++
auto nread = TRY(source_file->read(buffer));
TRY(destination_file->write(buffer));
```

It's a little clunky to have to create a Bytes or StringView from the
buffer's data pointer and the nread, and easy to forget and just use
the buffer. So, this patch changes the read() function to return a
Bytes of the data that were just read.

The other read_foo() methods will be modified in the same way in
subsequent commits.

Fixes #13687

Userland/Libraries/LibCore/InputBitStream.h

@@ -31,7 +31,7 @@ public:
 
     // ^Stream
     virtual bool is_readable() const override { return m_stream.is_readable(); }
-    virtual ErrorOr<size_t> read(Bytes bytes) override
+    virtual ErrorOr<Bytes> read(Bytes bytes) override
     {
         if (m_current_byte.has_value() && is_aligned_to_byte_boundary()) {
             bytes[0] = m_current_byte.release_value();