fix label squeezed bug

[TurkeyBilly]

Motivation

When using get_axis_label, label.shift_onto_screen(buff=MED_SMALL_BUFF) will squeeze labels into the original pre-set frame radius. This is very inconvenient when working with a zooming camera frame.
Therefore proposed to add a parameter set to False on default, since users who do not realize this function exists will cause buggy issues.

Proposed changes

• added a parameter ensure_on_screen to activate shift_onto_screen method for label

Test

Code:

        fr: CameraFrame = self.camera.frame
        fr.scale(2).shift(4*UP+6*RIGHT)
        common_plane_config = dict(
            x_range=[0, titrated, titrated/10],
            height=FRAME_HEIGHT*1.6, width=FRAME_WIDTH*1.6
        )

        plane = NumberPlane(
            **common_plane_config, y_range=[0, 14.0, 2.0],
        ).scale(0.5).shift(0.5*LEFT)
        plane.add_coordinate_labels()
        self.add(
            plane.get_x_axis_label("mL", direction=RIGHT),
            plane.get_y_axis_label("pH", direction=UP)
        )

        a_conentration_plane = NumberPlane(
            **common_plane_config, y_range=[0, 14.0, 2.0],
        ).scale(0.5).shift(0.5*LEFT + 7.5*UP)
        a_conentration_plane.add_coordinate_labels()
        a_conentration_plane.add(
            a_conentration_plane.get_x_axis_label("mL", direction=RIGHT),
            a_conentration_plane.get_y_axis_label("M", direction=UP)
        )

        ha_concentration_plane = NumberPlane(
            **common_plane_config, y_range=[0, 14.0, 2.0],
        ).scale(0.5).shift(13.*RIGHT + 7.5* UP)
        ha_concentration_plane.add_coordinate_labels()
        self.add(
            ha_concentration_plane.get_x_axis_label("mL", direction=UP),
            ha_concentration_plane.get_y_axis_label("M", direction=UP)
        )

        oh_concentration_plane = NumberPlane(
            **common_plane_config, y_range=[0, 14.0, 2.0],
        ).scale(0.5).shift(13.*RIGHT)
        oh_concentration_plane.add_coordinate_labels()
        self.add(
            oh_concentration_plane.get_x_axis_label("mL", direction=RIGHT),
            oh_concentration_plane.get_y_axis_label("M", direction=UP)
        )

        self.add(plane, a_conentration_plane, ha_concentration_plane, oh_concentration_plane)

Result: