update template literal types to support index signatures

[DetachHead]

https://devblogs.microsoft.com/typescript/announcing-typescript-4-4-beta/#symbol-template-signatures

Currently it just treats them as a string, but now that typescript 4.4 changes this, it should be changed in typescript-is as well

[samchon]

Another library typescript-json supports it.

https://github.com/samchon/typescript-json#runtime-validators