Add ProjectDim function

[lzj1769]

Thanks for this great package.

I am wondering if ArchR can provide a function to project matrix to low dimension,
for example, here is how Seurat does:

# If you wold like to observe genes that are strongly correlated with the first MDS coordinate
pbmc <- ProjectDim(pbmc, reduction = "mds")

thanks,

[jgranja24]

Hmmm this seems reasonable I will take a look further into this.