{{alias}}( value )
    Returns the matrix triangle string associated with a supported BLAS matrix
    triangle value.

    Parameters
    ----------
    value: any
        Matrix triangle value.

    Returns
    -------
    out: string|null
        Matrix triangle string.

    Examples
    --------
    > var out = {{alias}}( 'upper' )
    'upper'
    > out = {{alias}}( {{alias:@stdlib/blas/base/matrix-triangle-str2enum}}( 'upper' ) )
    'upper'

    See Also
    --------