types: avoid "interface can only extend object types with statically known members" error in TypeScript 4

[vkarpov15]

Fix #13775

Summary

In #13577, we removed FlatRecord from Schema definition because we didn't think it was necessary. And it doesn't look like FlatRecord is necessary in TypeScript 5, but for some reason is necessary in certain cases with TypeScript 4.

Will add FlatRecord back since it doesn't seem to break anything, and fixes #13577. But we will undo this change for 8.0, and we should make a note that we no longer support TypeScript 4.x or older.

Examples

[hasezoey]

Typescript can be weird sometimes, especially when trying to support multiple versions

[vkarpov15]

@hasezoey do you know of a way to set minimum TypeScript version without using peerDependencies?

[hasezoey]

do you know of a way to set minimum TypeScript version without using peerDependencies?

aside from keeping the minimal and installed typescript version in-sync, i dont know of a way. even this way will cause problems (because future typescript versions may make something invalid or change interfaces)

for typegoose i just set the minimal typescript version (the one mentioned in the readme / quick start guide) to be what is installed in the package.json (and use semver symbol ~) and only update the typescript version if required (like mongoose making a breaking type change (which happened quite often in the 5.11 to 6.something times)) or in major typegoose updates

[vkarpov15]

I guess the problem is that Mongoose doesn't require TypeScript, so there isn't a good way for us to indicate supported TypeScript version in package.json. We will just add that to the docs.