a703f5afb8
- This improves the memory usage of `FileStructureElementDiagnosticList` by avoiding lots of duplicate empty mutable maps. We can assume that most diagnostics lists are empty, since code is usually green. - I tested the memory consumption manually by opening all files in `org.jetbrains.kotlin.idea.k2.codeinsight.inspections` and waiting for analysis to finish for each file. With the change, the retained size of `FileStructureElementDiagnosticList` shrank from 63.39kB to 13.77kB.