Compile a list of NVDA commands unbound by default

[bhavyashah]

Is your feature request related to a problem? Please describe.

Currently, there does not appear to be a way to generate a list of unbound commands for which shortcuts can be assigned using NVDA's Input Gestures dialog. For context, I was reading https://github.com/nvaccess/nvda/issues/7695#issuecomment-546322858 and became curious about what other commands were available but unassigned by default. I searched for "unassign" and "unbound" in the User Guide and in the Input Gestures dialog and failed to find anything.

Describe the solution you'd like

There are two ways to resolve this, and I don't think those are mutually exclusive nor have I adequately thought through the merits and demerits of each. 1 Add a section in the User Guide listing all commands that are unbound by default but to which a gesture can be assigned. 2 Add a filter to the Input Gestures dialog - either some search syntax or an explicit control of some sort - that narrows down results to unbound commands only.

Describe alternatives you've considered

For the time being, I am going through the What's New document reading all entries containing the string "unbound" and making a mental compilation of all commands, added over the years, that are left unassigned by default. This is an evidently patchy and non-ideal means to access this information.

Additional context