add reverse converter

[bbrehm]

This does three things:

1. Fixes some bugs in the odb->flatgraph conversion. This probably didn't come up in our tests so far, because the bugs were in the containedNode conversion code, and these are only used post improvements in codescience.
2. Remove the legacyId from the conversion code. We can consider adding that in again?
3. Add code to convert flatgraph to odb. Main known limitation at this point is the issue that the file format doesn't store the name of edge properties, so this cannot be faithful.

When testing, note that we don't recreate the odb indices on conversion. Odb notices that, and then eagerly deserializes all nodes. If any nodes have latent schema violations, then this will immediately throw on cpg loading, as opposed to the behavior on loading a "real" cpg. This came out because I used a very old ocular version for testing, and CONTAINS edges in IMPLICIT_CALL nodes are new ;)

This still contains some debug code that I'll remove before merging.

[mpollmeier]

related: ShiftLeftSecurity/overflowdb#439

[mpollmeier]

i guess this is part of your "debug output" that will be removed / censored before merge? :)

[mpollmeier]

Seems to work!
I created a cpg with joern-flatgraph:

joern> importCode("/home/mp/tmp/cpgtesting/hsl-springboot/HelloShiftLeft")

Then converted with this PR to overflowdb:

odb-convert/target/universal/stage/bin/flatgraph-odb-convert -r /home/mp/Projects/shiftleft/joern/workspace/HelloShiftLeft/cpg.bin /home/mp/Projects/shiftleft/joern/workspace/HelloShiftLeft/cpg.bin.odb

Then loaded into joern master (to verify that it'll fail):

joern> importCpg("/home/mp/Projects/shiftleft/joern/workspace/HelloShiftLeft/cpg.bin.odb")
...
Error loading CPG
java.lang.RuntimeException: java.lang.RuntimeException: Edge REACHING_DEF does not support property `EDGE_PROPERTY`.

Then again on joern master with ShiftLeftSecurity/overflowdb#439 applied:

joern> importCpg("/home/mp/Projects/shiftleft/joern/workspace/HelloShiftLeft/cpg.bin.odb")
...

val res0: Option[io.shiftleft.codepropertygraph.generated.Cpg] = Some(value = Cpg (Graph [45618 nodes]))

joern> cpg.graph.edges.size
val res1: Int = 350033

joern> cpg.graph.edges.count(_.propertiesMap.size == 1)
val res2: Int = 72812

joern> cpg.graph.edges.count(_.propertiesMap.size == 2)
val res3: Int = 0

[mpollmeier]

after you removed all swear words

[bbrehm]

Swear words censored, added a debug option to dump the manifest (very useful if something goes wrong).