The outline is incorrect for expr2.f90/a.f90

[certik]

For the code from #55, here is the outline that I can see for expr2.f90:

There are several issues:

• The root node is "a", but rather the root node should be "expr2".
• There are two symbol "x". The first one points to line 2, as it should. The second one points to line 4, which is empty. It likely is pointing to line 4 in file a.f90, but this symbol should not be part of the outline at all.

[dylon]

We need to update --show-document-symbols to use the DocumentSymbol schema from LSP to represent the symbol hierarchy. That should correct the rendition of the outline list. We currently use the SymbolInformation schema which has been deprecated. Although we supply the correct file path to each symbol's definition, there is likely a bug in VSCode that is makes it not navigate to the correct location of external symbol definitions from the outline list. I conjecture that we can either correct it by migrating to the DocumentSymbol schema or by filtering-out symbols that do not belong to the current document.