extmod/btstack: Include value handle in client read/write events.

This replaces the previous pending operation queue (that used to also be
shared with pending server notify/indicate ops) with a single pending
operation per connection. This allows the value handle to be correctly
passed to the Python-level events.

Also re-structure GATT client event handling to simplify the packet handler
functions.

Signed-off-by: Jim Mussared <[email protected]>

Author: jimmo

docs/library/bluetooth.rst

@@ -183,12 +183,10 @@ Event Handling
                 conn_handle, value_handle, char_data = data
             elif event == _IRQ_GATTC_READ_DONE:
                 # A gattc_read() has completed.
-                # Note: The value_handle will be zero on btstack (but present on NimBLE).
                 # Note: Status will be zero on success, implementation-specific value otherwise.
                 conn_handle, value_handle, status = data
             elif event == _IRQ_GATTC_WRITE_DONE:
                 # A gattc_write() has completed.
-                # Note: The value_handle will be zero on btstack (but present on NimBLE).
                 # Note: Status will be zero on success, implementation-specific value otherwise.
                 conn_handle, value_handle, status = data
             elif event == _IRQ_GATTC_NOTIFY: