This commits moves all `.d.ts` files from `ext/*` to `cli/tsc/dts`.
Due to TSC snapshot removal, `cargo publish` is now erroring out,
unable to find the declaration files. These files were moved to
"cli/tsc/dts", because it's much easier than keeping them in
extension directories, while still providing them compressed
or uncompressed depending on the build type.
This change aims to replace all relative import specifiers targeted at
`tests/util/std` with mapped ones (using a `deno.json` file). Towards
updating the `std` git submodule.
