Add info about gvfs sparse to gvfs health verb

I've been playing with the gvfs health verb a bit (very cool!) with the gvfs sparse functionality turned on, and I was wondering how feasible it would be to incorporate the current status of the sparse projection to it? For example:

D:\mono\src>gvfs health
Gathering repository data...

Health of directory:
Total files in HEAD commit:           2,614,142 | 100%
**Suggestion: total files in head commit currently being projected?**

Files managed by VFS for Git (fast):     64,036 |   2%
Files managed by Git:                         5 |   0%

Total hydration percentage:                         2%
**Suggestion: Total hydration of current projection:**

Most hydrated top level directories:
 35,065 / 131,728 | warehouse
 25,073 / 74,634  | otools
  1,844 / 2,183   | cloudbuildtools
    703 / 65,177  | collateral
    559 / 3,040   | engtools

Repository status: OK

TBC: I 100% don't think we should add this if it is going to be expensive to compute, but if somehow that data could be available easily that would be really nice!