Projects can now add the following config fragment to their .clangd:
Style: IncludeDelimiter: AlwaysBrackets
to force headers inserted via the --header-insertion=iwyu mode to have
<> around them in all cases, rather than relying on whether the header
was included via -isystem or not.
This solution does not allow forcing "" in all cases, nor does it affect
other clang tools like clang-format.