commands/init: Make validation of positional arguments happen in the arguments package. Refactor away unneeded code.

[SarahFrench]

This PR refactors how unexpected positional arguments supplied to the init command are validated.

The ModulePath function is the result of how commands used to have positional DIR arguments, which allowed users to use a directory other than the directory where the CLI was being used. When that DIR argument was replaced with the -chdir flag, we end up with the code below. Whereas before it would use that argument to determine the path to the root module, now it just validates that the DIR argument isn't mistakenly being used and then returns details about the current working directory:

terraform/internal/command/command.go

Lines 62 to 75 in 78a3330

	func ModulePath(args []string) (string, error) {
	// TODO: test
	if len(args) > 0 {
	return "", fmt.Errorf("Too many command line arguments. Did you mean to use -chdir?")
	}
	path, err := os.Getwd()
	if err != nil {
	return "", fmt.Errorf("Error getting pwd: %s", err)
	}
	return path, nil
	}

It doesn't make sense to validate unexpected positional arguments here; that should be done in the arguments package.

This PR updates the code for parsing flags and arguments used with the init command to assert that no positional arguments are expected. If that validation passes, there are no args, then we don't need to return an empty list of args to the command implementation through the Args field removed in this PR.

Now that no args are being passed into the ModulePath function it's just a fancy way of calling os.Getwd. The Meta contains details about the working directory, so I've replaced use of the ModulePath function with the relevant method.

This is work towards deleting the ModulePath function from the codebase 💪🏻

Target Release

1.16.x

Rollback Plan

• If a change needs to be reverted, we will roll out an update to the code within 7 days.

Changes to Security Controls

Are there any changes to security controls (access controls, encryption, logging) in this pull request? If so, explain.

CHANGELOG entry

• This change is user-facing and I added a changelog entry.
• This change is not user-facing.