Bitmap label ascent descent

[FoamyGuy]

This implements the changes required in bitmap_label.py to use the ascent and descent feature which was recently added to Adafruit_CircuitPython_Bitmap_Font

The analogous PR for the regular label was #102

I tested on a PyPortal with this code:

import board
from displayio import Group
from adafruit_display_text import bitmap_label
from adafruit_bitmap_font import bitmap_font

font = bitmap_font.load_font("/fonts/forkawesome-36.pcf")
w,h,dx,dy = font.get_bounding_box()

glyphs = "".join(chr(0xf000 + i) for i in range(8))

group = Group()
label = bitmap_label.Label(font=font, text=glyphs, background_color=0x111111)
label.anchor_point = (0, 0)
label.anchored_position = (0,0)

group.append(label)
board.DISPLAY.show(group)
while True:
    pass

[jposada202020]

Tested in WIO terminal Using CP 6.0.1, with code included. works good.

[jepler]

No testing performed