Pasting more or less sizable text into ESP8266 REPL leads to random chars
missing in the received input. Apparent cause is that using RTOS messages
to pass individual chars one by one is to slow and leads to UART FIFO
overflow. So, instead of passing chars one by one, use RTOS msg to signal
that input data is available in FIFO, and then let task handler to read
data directly from FIFO.

With this change, lost chars problem is gone, but the pasted text is
truncated after some position. At least 500 chars can be pasted reliably
(at 115200 baud), but 1K never pastes completely.