is<TypeIdentifier> functions mark argument as `never` when they returns `false`.

[coolsoftwaretyler]

Bug report

• [x] I've checked documentation and searched for existing issues and discussions
• [x] I've made sure my project is based on the latest MST version
• [x] Fork this code sandbox or another minimal reproduction.

Sandbox link or minimal reproduction code

https://codesandbox.io/p/sandbox/isoptional-type-bug-repro-9h8cqg?file=%2Fsrc%2Findex.ts%3A11%2C6-12%2C1

Describe the expected behavior

x shouldn't be type never. Should be ISimpleType<number>

Describe the observed behavior

TypeScript thinks x is of type never:

[dbstraight]

The same is true of others: isIdentifierType, isLiteralType, isPrimitiveType, isReferenceType, isUnionType, maybe others I haven't tried.

[coolsoftwaretyler]

Updated the title to reflect that (pun intended). Thank you!