Move common indexeddb methods out of dom implementations (#38101)

A lot of shared functions were scattered around the dom files; I moved
them into `indexed_db.rs` for clarity.

Fixes: Nothing to my knowledge, just a cleanup

Signed-off-by: Ashwin Naren <arihant2math@gmail.com>

components/script/lib.rs

@@ -34,6 +34,7 @@ mod dom;
 mod canvas_context;
 mod canvas_state;
 pub(crate) mod fetch;
+pub(crate) mod indexed_db;
 mod init;
 mod layout_image;