gdb/debuginfod: Improve progress updates

gdb/debuginfod: Improve progress updates

If the download size is known, a progress bar is displayed along with
the percentage of completion and the total download size.

  Downloading separate debug info for /lib/libxyz.so
  [############                                      ]  25% (10.01 M)

If the download size is not known, a progress indicator is displayed
with a ticker ("###") that moves across the screen at a rate of 1 tick
every 0.5 seconds.

  Downloading separate debug info for /lib/libxyz.so
  [         ###                                                      ]

If the output stream is not a tty, batch mode is enabled, the screen is
too narrow or width has been set to 'unlimited', then only a static
description of the download is printed. No bar or ticker is displayed.

  Downloading separate debug info for /lib/libxyz.so...

In any case, if the size of the download is known at the time the
description is printed then it will be included in the description.

  Downloading 10.01 MB separate debug info for /lib/libxyz.so...