Support TypeScript 5

[ntucker]

https://github.com/microsoft/TypeScript/wiki/API-Breaking-Changes#typescript-50

[hanayashiki]

If this library doesn't work with ts5, how it specifies its dependency as 'next'?

https://github.com/sandersn/downlevel-dts/blob/master/package.json#L21

I noticed this because every day I try to update my dependencies, I download a latest build of typescript for nothing.

[dannolan]

Yeah noting the above we are constantly downloading the nightly of typescript