Make OptionValueSource a string with well-known values for auto-complete

[shadowspawn]

Pull Request

Problem

Authors are allowed to use their own strings for OptionValueSource, but the usual range will just be the values that Commander uses. The TypeScript typing only listed the Commander values to support the primary use, and get autocomplete in the editor.

Solution

Use a well-known "trick" to specify a string with some known values. The known values are offered for auto-complete by VSCode, and TypeScript allows other values too.

This was prototyped in https://github.com/commander-js/extra-typings

References:

• Literal String Union Autocomplete microsoft/TypeScript#29729
• https://github.com/sindresorhus/type-fest/blob/main/source/literal-union.d.ts
• https://github.com/sindresorhus/type-fest/blob/main/source/primitive.d.ts

ChangeLog

• fix: update OptionValueSource to allow any string to match supported custom use

[abetomo]

LGTM