Support `"<user.search_engine>"` action

[pokey]

Eg "google air" to search for the target in Google

We should probably just let users define this one in user space. We'd proceed as follows:

• Add get_text action to public cursorless api #452
• Create a Recipes page on the wiki
• Add the recipe below to the wiki

{user.search_engine} scout <user.cursorless_target>:
    text = user.cursorless_get_text(cursorless_target)
    user.search_with_search_engine(search_engine, text)

[pokey]

Done. See https://github.com/cursorless-dev/cursorless/wiki/Recipes