mpsqa.lint: add back missing location information to saved results

[alexanderpann]

This is a follow-up of #184 where a forgot to adapt the saved messages and I also fixed a few linters where the error reporting was missing information. With this new change, you can also navigate in the checker results to files, nodes, models and modules. Files can now be returned as a result in linters.

[danielratiu]

if I do not have generated the linter, the result is an exception due to the "Result.location" being null

---

java.lang.NullPointerException: Cannot invoke "Object.toString()" because the return value of "org.mpsqa.lint.generic.util.Result.location()" is null
at org.mpsqa.lint.generic.typesystem.ViolationsReporterUtils.reportViolations(ViolationsReporterUtils.java:28)
at org.mpsqa.lint.generic.typesystem.check_checkableScript_NonTypesystemRule.applyRule(check_checkableScript_NonTypesystemRule.java:39)
at jetbrains.mps.newTypesystem.context.typechecking.IncrementalTypechecking.applyRuleToNode(IncrementalTypechecking.java:157)
at jetbrains.mps.newTypesystem.context.component.NonTypeSystemComponent.lambda$applyNonTypesystemRulesToNode$2(NonTypeSystemComponent.java:345)
at jetbrains.mps.newTypesystem.context.typechecking.IncrementalTypechecking.runApplyRulesTo(IncrementalTypechecking.java:166)
at jetbrains.mps.newTypesystem.context.component.NonTypeSystemComponent.applyNonTypesystemRulesToNode(NonTypeSystemComponent.java:320)
at jetbrains.mps.newTypesystem.context.component.NonTypeSystemComponent.applyRulesToRoot(NonTypeSystemComponent.java:308)
at jetbrains.mps.newTypesystem.context.component.NonTypeSystemComponent.lambda$applyNonTypeSystemRulesToRoot$1(NonTypeSystemComponent.java:293)
at jetbrains.mps.languageScope.LanguageScopeExecutor.execWithModelScope(LanguageScopeExecutor.java:63)
at jetbrains.mps.languageScope.LanguageScopeExecutor.execWithModelScope(LanguageScopeExecutor.java:43)
at jetbrains.mps.newTypesystem.context.component.NonTypeSystemComponent.applyNonTypeSystemRulesToRoot(NonTypeSystemComponent.java:293)
at jetbrains.mps.newTypesystem.context.typechecking.IncrementalTypechecking.applyNonTypesystemRulesToRoot(IncrementalTypechecking.java:227)
at jetbrains.mps.newTypesystem.context.typechecking.BaseTypechecking.applyNonTypesystemRulesToRoot(BaseTypechecking.java:142)
at jetbrains.mps.newTypesystem.context.typechecking.BaseTypechecking.applyNonTypesystemRulesToRoot(BaseTypechecking.java:135)
at jetbrains.mps.typesystemEngine.checker.NonTypesystemChecker.lambda$getErrors$1(NonTypesystemChecker.java:57)

<<<<<<<<<<<<<

In general, couldn't we use another default `value for location besides "null"? the code (many places in ResultEntry behavior) is quite heavily accessing resultLocation and might cause NPEs ...

[alexanderpann]

I only saw two potential cases where it could be null, so I just added two null checks. In ResultEntry, we need try catch blocks anyway, so NullPointers are not an issue there.

[ratiud]

looks good now - thank you!