Try to restore high res image import.

[kimsjune]

This aims to fix #8381 by restoring image.name option for readPNG() and consequently Read10X_Image(). The master branch version has "tissue_lowres_image.png" hard-coded. This was not the case in an earlier version, so I just copied it back. There is a scale factor error if the high res image is used, which can be mitigated by:

hires <- Read10X_Image(paste0(data.dir,'spatial',sep=''),image.name='tissue_hires_image.png')
hires@scale.factors$lowres = hires@scale.factors$hires

Also mentioned here.

Hope this can help.