FTM: use last_direction_bits and axis did_move for direction and motion

[narno2202]

Description

The goal is to use the already defined variables axis_did_move and last_direction_bits with FT_MOTION.

1. axis_did_move replace axis_moving_flags as is.
2. last_directions_bits replace axis_move_dir as is but it's updated if necessary on every call to ftMotion.stepper().
3. Add a preprocessor directive for discard_current_block() in stepper.h, as it's utilized only with standard motion.

Changes are independent of the printer type and now common to the 2 motion systems.
This change allows universal axis_is_moving(const AxisEnum real) and axis_direction(const AxisEnum real) functions.

It's totally transparent for people having only FT_MOTION as a motion system; it diminishes flash size if you have both motion systems.

Requirements

Benefits

Configurations

Related Issues

None

[narno2202]

CI fails for Rambo with "The data size (8847 bytes) is greater than maximum allowed (8192 bytes)".
Perhaps

#define FTM_BUFFER_SIZE             128   // Window size for trajectory generation, must be a power of 2 (e.g 64, 128, 256, ...)
                                            // The total buffered time in seconds is (FTM_BUFFER_SIZE/FTM_FS)
#define FTM_FS                     1000   // (Hz) Frequency for trajectory generation.
#define FTM_MIN_SHAPE_FREQ           20   // (Hz) Minimum shaping frequency, lower consumes more RAM 

should be adapted in the test build for this motherboard.
With my config,RAM size is the same with this PR and current bugfix, only flash size is lower with this PR.

[oliof]

Setting FTM_BUFFER_SIZE to 64 and FTM_MIN_SHAPE_FREQ TO 35 should clear enough RAM for ATMEGA2560