I often find myself inside a collection in Lightroom and I want to jump to the "All Photographs" view leaving my selection intact. I can do this via the mouse by going to the Catalog panel and clicking on the "All Photographs" collection.
Is there a keyboard shortcut? Or perhaps a way to otherwise make this accessible via keyboard?
Based on Adobe's list of keyboard shortcuts there is no shortcut for changing to the 'All Photographs' collection (or any collection except for the quick collection) but you can use 'Tab' to show the side panels if hidden, and then make the 'Catalog' section of the left side panel visible if it isn't by using Ctrl + Shift + 1 on Windows (and I assume Command + Ctrl + 1 on Mac).
Above the film strip there is a black bar, inside of it is your main window , secondary window, grid bar, 'go back' and go forward. Right next to it is your current folder and current selected file.
At the end of your current selected filename, there is a little triangle where you can click and it will prompt you a drop down menu of folders you might want to access to. Select the 'All Photograph' from there and voila, you gain access to the "All Photography" folder and that is the quickest method I think.
There is a plugin that you can try out called Any Source plugin. You can download it and install (instructions can be found from the above link) : Source
