This makes them available for use by other language servers.
Also as a bonus, update the Shell language server to discover some
symbols and add go-to-definition functionality :^)
(...and ASSERT_NOT_REACHED => VERIFY_NOT_REACHED)
Since all of these checks are done in release builds as well,
let's rename them to VERIFY to prevent confusion, as everyone is
used to assertions being compiled out in release.
We can introduce a new ASSERT macro that is specifically for debug
checks, but I'm doing this wholesale conversion first since we've
accumulated thousands of these already, and it's not immediately
obvious which ones are suitable for ASSERT.
FileDB wraps the access to the contents of project files.
When asked to fetch a file, FileDB will either return its in-memory
model of the file if it has been "opened" by the language-server
protocol, or otherwise fetch it from the filesystem.
Previously, the cpp language server did not pledge "rpath" and got
access to the contents of files whenever they were opened by the
language client.
However, features like inspection of header files require the language
server to get the content of files that were not opened by the client.
The language server now pledges rpath but makes sure to only unveil
the project's directory and /usr/include.
