trend_plot_shiftDirection: Trend plot of grid shifting effect
In MPE-Lab/TIPC: Tumor-Immune Partitioning and Clustering (test)

Plotting the changes in TIPC metric count as the grid shfited to 4 other directions i.e. origin + left + right + uppper + down

trend_plot_shiftDirection(
  root_dir = NULL,
  hex_len_range = NULL,
  hex_len_stepsize = NULL,
  pdf_width = 9,
  pdf_height = 12
)

`root_dir`	A directory path pointing to the parent directory of the ouptput folders containing TIPC metric counts generated by `count_TIPC_cat` at various hexagonal lengths.
`hex_len_range`	A vector of 2 integer number indicating the range of hexagonal length. If unspecified (NULL), all found TIPC result folders of different hexagonal lengths will be processed. All hex_len data will be collapsed into 5 directions.
`hex_len_stepsize`	An integer indicating the step size of hexagonal length. If unspecified (NULL), all found TIPC result folders of different hexagonal lengths will be processed.
`pdf_width, pdf_height`	the width and height of the graphics region in inches. The default values are 9 and 12; inherited from `pdf`