Review boolean declaration option parsing

[aciccarello]

In PR #845, a question came up about the parsing of boolean declaration options.

typedoc/src/lib/utils/options/declaration.ts

Lines 80 to 82 in 7799a89

	case ParameterType.Boolean:
	value = (typeof value === void 0 ? true : !!value);
	break;

The original code was written to return true if the option is undefined and the truthy value of the option otherwise. It was noted by @Gerrit0 that typeof will always return a string, therefore the typeof check will always return false and the expression should be simplified to value = !!value;.

Since there is likely a bug in this code, it should be thoroughly reviewed and corrected.

[Gerrit0]

I spent some time looking into this and have determined that either value === undefined ? true : !!value or !!value is acceptable.

In the first case, we add a special case for converting an undefined value to true. This is somewhat consistent with other parts of the code base like setFlag(flag) will set the flag to true for a signature setFlag(flag: Flag, value = true).

The current behavior ignores this special case, the existing argument readers correctly handle it with the current logic, and the special case introduces a footgun if a user has a JS config file that returns boolean value as undefined (which normally coerces to false) turning true.

With this in mind, I think it is best left as is, with no special case.