Improves DimHeatmap documentation and default behavior when fast=FALSE (Issue #9810)

[dkcoxie]

Clarifies documentation to specify that figure legends are currently not displayed when fast=TRUE but added titles with PC numbers to ggplot outputs so that both PC number and figure legends can be displayed on the same plot, plus option to move position of shared patchwork legend when combine=TRUE to resolve Issue #9810

[dkcoxie]

In preparing teaching materials geared toward beginners, we found that the default behavior of DimHeatmap() either displays no figure legend but includes the PC number as panel titles (default fast=TRUE) OR allows the figure legend to be shown for the ggplot2 output doesn't display the PC number for each panel (when fast=FALSE).

The Proposed changes to theDimHeatmap() function clarify the documentation regarding when a figure legend will be displayed, add PC labels as individual figure titles for the ggplot2 outputs, and allow for the position of the figure legend to be moved when the ggplots are combined into a single patchwork output.