New Progress Bars

This implements a new progress bar, drawing on our work in #196 and your other more recent version (ecb590e). It uses the draw algorithm from the former, and the updated styling, matcher regexp, faces, etc. from the latter. It is a simple, fast, pixel-perfect progress bar, with a fixed overall bar width. It uses specified space (on the `[` and `]` chars) and the bare minimum of allocations from replacing string displays: - zero, if the completion bar is empty, full, or falls adjacent to or inside the stats text, as occurs in more than 50% of the cases; - one, otherwise The stats text can be edited, visited with point, copied, etc. I also added a parent face `org-modern-progress`. This is needed because it is important for all face settings that alter font (`:height`, `:weight`, etc.) to be set _consistently_ across both `complete` and `incomplete`. I made that parent face inherit from `fixed-pitch` (also important for consistent bar width). I also made it bold and reduced the height, and slightly lightened the incomplete face to avoid conflicts with somewhat less dark theme backgrounds. Here's how it looks: <img width="233" alt="image" src="https://github.com/minad/org-modern/assets/93749/79a403f9-e911-42bb-84f3-226831e36f6f"> The one price for a pixel-perfect completion bar is that the start of the stats text moves slowly by <1 char width, but i) the numbers themselves will move too as they change size (`9` -> `10`), and ii) bars are usually not lined up on top of each other so alignment isn't a top concern. Another PR can consider overall alignment of progress bars and tags within the window. Let me know if you are still encountering any bar movement on item checkoff.