Support explicit type sorting

[IanVS]

Closes https://github.com/IanVS/prettier-plugin-sort-imports/issues/35

Adapted from https://github.com/trivago/prettier-plugin-sort-imports/pull/153, by @Xenfo.

This adds a new special string, <TYPES> that can be added to the importOrder array. When used, it will cause type imports to be sorted as specified by its location in the array.

Notes:

• If it is used, it will disable importOrderCombineTypeAndValueImports, throwing a warning if both are used. This is because:
• We will split apart type and value import declarations if <TYPES> is used, so that types can be sorted appropriately.
• Thinking towards the next breaking change when we remove options, I think the default will be to enable importOrderCombineTypeAndValueImports, and this change will give users a good way to opt-out of that behavior if they want, by specifying the location for <TYPES>.

[IanVS]

@fbartho @blutorange I'd love to get your thoughts on this change before merging.