A way to show the values of all defined variables

[typeless]

I am currently using my own cmd print-vars for this purpose.
It would be convenient if there is such a builtin for debugging.

[andyjp94]

Would this be a useful CLI structure for accessing the variable values?

1. List variables that are available for all commands

task --vars=global

2. List all variables that are available on linux

task --vars=linux --vars=global

3. List variables that are available for a specific command and for linux

task --vars=${CMD_NAME} --vars=linux

[andreynering]

@andyjp94 Probably something like --show-vars would be better, since --vars=* feels like setting a variable.

Also, the other options should probably have they own flags, like --os=*.

[clintmod]

maybe just do this in #931

[andreynering]

Closing as a duplicate of #931