Deep suggestions based on task names

[lihaoyi]

This PR adds an addition suggestion to the Try ... to see what's available error message based on the task names present in the entire build.

Before:

$ ./mill -i dev.run example/scalabuilds/10-scala-realistic -i Compilee
Cannot resolve Compilee. Try `mill resolve _` to see what's available.

After:

$ ./mill -i dev.run example/scalabuilds/10-scala-realistic -i Compilee
Cannot resolve Compilee. Try `mill resolve _` or `mill resolve __.compile` to see what's available.

This should help in the common case where someone runs a task with the correct name but in the wrong module. We do a fuzzy match, so even if there's a small typo we still are able to give a suggestion. This is complementary to the existing help message, which is useful when the user runs a task with the wrong name but in the correct module

The way this works is that we capture all the non-command task names in the Discover macro, and when a user runs a task that fails to resolve, we look at the last segment of the query and run a fuzzy search against the set. If a fuzzy match is found, we suggest to the user to run mill resolve __.foo so they have a way to see what the fully-qualified name of the task they were trying to run, and run it. Given the typical build would have O(10s) to O(100s) of modules at most, we can expect even the most verbose mill resolve __.foo outputs to be small enough that the user can browse through and find what they want