Allow readonly array as parameter to .aliases(), .parse(), .parseAsync()

[shadowspawn]

Pull Request

Problem

readonly array cannot be passed directly as parameter to .aliases(), .parse(), or .parseAsync().

Work-around: make a modifiable copy, like by calling .slice().

Following pattern used in #1667 for .choices().

Solution

No implementation changes needed, just declaration and tests.

• add readonly to TypeScript declaration file
• add readonly test to TypeScript tests
• add readonly tests of JavaScript implementation

ChangeLog

• changed: allow passing readonly string array to .parse()
• changed: allow passing readonly string array to .parseAsync()
• changed: allow passing readonly string array to .aliases()

[abetomo]

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