Add alias description to prompt-toolkit autosuggestion

We have description in suggestion in prompt-toolkit:

grep -i<Tab>
# -i
# Perform case insensitive matching.  By default, grep is case sensitive.

But:

@aliases.register
def _ali1():
    """ali1 description"""
    echo 1

@aliases.register
def _ali2():
    """ali2 description"""
    echo 2

ali<Tab>
# ali1 ali2  # No description

Expected:

ali<Tab>
# ali1 
# ali1 description
# ali2
# ali2 description

For community

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