- As mentioned in KT-60570, memory consumption in cached symbol names
providers is caused partially by lots of instances of empty mutable
sets. This commit replaces such sets with the `emptySet()` singleton.
- This improvement also makes sense for callable names because the IDE
"package names with top-level callables" set currently contains all
package names in the project.
- In my local tests of the `setUp` Find Usages performance test, the
retained size of `FirDelegatingCachedSymbolNamesProvider` is cut down
from 208MB to 170MB by the empty class name set optimization, and from
170MB to 115MB by the empty callable name set optimization.
Marco Pennekamp
017784d24f