feat: implement task sorting with --sort flag

[pd93]

Fixes #946

This PR implements custom sorting for tasks using a new --sort flag. This will work with any of the commands that output a list of tasks. i.e.

• task --list
• task --list --silent
• task --list --json
• task --list-all

The --sort flag will accept a string that specifies the sort order. The following values are supported:

• default - The same as alphanumeric, but root tasks (with no namespace) will be always appear first.
  • This is the current sorting behavior
• none - No sorting. Tasks will appear in the order they are defined in the taskfile
  • If multiple taskfiles are used, they will be traversed in lexicographical order of the taskfile path.
• alphanumeric - Sorts tasks alphabetically by name ignoring the files they are defined in.

The implementation for this was quite complex so here is a bullet point summary of the changes:

• The contents of copy.go has been moved to a new package in internal/deepcopy so that it can be more easily reused
• We have two other new packages:
  • internal/sort - Contains the task sorting interface and implementations
  • internal/orderedmap - Contains a generic ordered map implementation
• Refactored taskfile.Tasks to use the orderedmap implementation
• Refactored taskfile.Vars to use the orderedmap implementation
  • This replaces the custom ordered map that was previously used
  • I had to do some interesting things here because most uses of taskfile.Vars use a pointer. When this pointer is nil, the method on the underlying OrderedMap cannot be called (because of how embedding works in Go). I've simply added some wrapper methods on taskfile.Vars to handle these cases which do nil checks before calling the underlying method. This is not an issue with taskfile.Tasks because they aren't implemented with a pointer.

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Side note... this would be so much nicer if we had golang/go#56413 in Go 😛

[andreynering]

Nice work! 👏

This flag needs to be mentioned on the API page. Other than that, this is ready to be merged.