The Locator now keeps a cache of the declared symbol in a document.
The language client updates that cache whenever it gets an update from
the language server about declared symbols.
This allows searching for symbol declarations in the Locator, in
addition to file names.
Closes#5478
Now that WindowServer broadcasts the system theme using an anonymous
file, we need clients to pledge "recvfd" so they can receive it.
Some programs keep the "shared_buffer" pledge since it's still used for
a handful of things.
