add point_shape argument

[Yunuuuu]

This commit just enable the customization of point shape The current version (without point_shape argument) ofter return a plot with large point:

scater::plotReducedDim(
    sce_clean,
    dimred = "UMAP",
    colour_by = "Sample",
    point_size = 0.01,
    point.padding = 0,
    force = 0,
    rasterise = TRUE
) 

By adjusting to the point_shape argument we can produce a plot with smaller point:

scater::plotReducedDim(
    sce_clean,
    dimred = "UMAP",
    colour_by = "Sample",
    point_shape = 16,
    point_size = 0.01,
    point.padding = 0,
    force = 0,
    rasterise = TRUE
)

[alanocallaghan]

Looks good! Could you document point_shape in R/plotPlatePosition.R and R/plotReducedDim.R please?

[Yunuuuu]

I have added the document and add a link to vignette("ggplot2-specs"), so users can easily see which shape integer or string to use.

Thanks for the development of the excellent and practicable single-cell package, hope this commit can be helpful.

[alanocallaghan]

Thanks for the excellent contribution!