Implement a basic way for read() to block.

FileHandle gets a hasDataAvailableForRead() getter.
If this returns true in sys$read(), the task will block(BlockedRead) + yield.
The fd blocked on is stored in Task::m_fdBlockedOnRead.
The scheduler then looks at the state of that fd during the unblock phase.

This makes "sh" restful. :^)

There's still some problem with the kernel not surviving the colonel task
getting scheduled. I need to figure that out and fix it.

Kernel/Console.cpp

@@ -21,6 +21,11 @@ Console::~Console()
 {
 }
 
+bool Console::hasDataAvailableForRead() const
+{
+    return false;
+}
+
 ssize_t Console::read(byte* buffer, size_t bufferSize)
 {
     // FIXME: Implement reading from the console.