Migrate CLI module to match Fyne CLI tools

[sdassow]

Description:

As a first step towards merging with fyne tools, only replace the CLI module, and should not change behaviour otherwise.

Checklist:

• Tests included.
• Lint and formatter run with no errors.
• Tests all pass.

Where applicable:

• Public APIs match existing style.
• Any breaking changes have a deprecation path or have been discussed.
• Updated the vendor folder (using go mod vendor).

[andydotxyz]

This appears to be a breaking change - any parameters passed with the single-dash prefix will no longer work as it's moved to two. Can we support both to avoid this break?
[✗] invalid value "test" for flag -app-build: parse error

[sdassow]

This appears to be a breaking change - any parameters passed with the single-dash prefix will no longer work as it's moved to two. Can we support both to avoid this break? [✗] invalid value "test" for flag -app-build: parse error

Hm, are you sure? The -app-build in your example fails because it's expecting a number.
It works for me as expected with single and double dash options.