remove most uses of as any in typescript

- replaced many uses of `as any` with another more specific cast `as T`
- filled in missing typed for items that needed to be typed
  - new runtime code was added where necessary to satisfy the new types with comments
- added missing theme variable "sidebar-active" to the Theme variables
- forms using `react-hook-form` are now typechecked
- changed some instances of `target` into `currentTarget` while removing `as any` assertions

src/components/common/messaging/attachments/AttachmentActions.tsx

@@ -18,7 +18,8 @@ export default function AttachmentActions({ attachment }: Props) {
     const open_url = `${url}/${filename}`;
     const download_url = url.replace('attachments', 'attachments/download')
 
-    const filesize = determineFileSize(size as any);
+    // for some reason revolt.js says the size is a string even though it's a number
+    const filesize = determineFileSize(size as unknown as number);
 
     switch (metadata.type) {
         case 'Image':