specs: Better error messages for badly quoted specs (#41805)

If you are calling Spack from the python API, you might have written something like this
before #41529:

```
find = SpackCommand("find")
find('--format={name}', 'saxpy@1.0.0', '+rocm', 'amdgpu_target="gfx90a"')
```

But with the breaking change in #41529, you should write:

```
find = SpackCommand("find")
find('--format={name}', 'gromacs', '+rocm', 'amdgpu_target=gfx90a')
```

Note that we don't need quotes in Python strings, and that this is what would come in
via argv if you typed a quoted variant on the CLI.

The error messages for strings like this are not great -- you get something like this:

```
==> No package matches the query: gromacs+rocm amdgpu_target="gfx90a"
```

Which doesn't indicate that the issue might be your quoting. This is because we were
simply outputting the argv we got, instead of using spec.format() to output the error
message. This PR fixes such errors to use `spec.format()` and to look like this:

```
==> No package matches the query: gromacs+rocm amdgpu_target='"gfx90a"'
```

So users should have an easier time understanding that Spack considers the variant value
to contain quotes here.

- [x] update ConstraintAction to store parsed Specs
- [x] refactor commands to display formatted parsed Specs instead of raw input

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