Description

#70843 and #70434 have created unnecessary friction for i18n functions. Reassigning the values to the result of i18n functions is a common and legitimate case, and this PR breaks that.

The return of i18n functions should be a string, not a string literal, because at runtime, it's not actually the English text that the type depicts. There is no use of that generic for these i18n functions.

Step-by-step reproduction instructions

This code should not have any TS errors

type Code = 'code-1' | 'code-2';

const errorCode: Code = 'code-1';

let message = __( 'Some default message' );

switch ( errorCode ) {
	case 'code-1':
		// This reassignment errs
		message = __( 'An error occurred' );
             // ^^^^^^^ "Type 'TranslatableText<"An error occurred">' is not assignable to type 'TranslatableText<"Some default message">'."
		break;
	default:
		message = __( 'Unknown error occurred' );
}

Screenshots, screen recording, code snippet

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Environment info

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Please confirm that you have searched existing issues in the repo.

• Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

• Yes

Please confirm which theme type you used for testing.

• Block
• Classic
• Hybrid (e.g. classic with theme.json)
• Not sure