[DMN Designer] Java Function is context after reopening

Spotted during DROOLS-2262 review, however probably it is not related.

If user save and reopen expression that is java function, the designer renders it as context expression after reopening. See the attached screenshots, there is unexpected result row after reopening.

Manual PR check

• Save and reopen BKM, with java function
• Save and reopen BKM, with PMML function
• Save and reopen BKM, with feel function
• Save and reopen Decision, with java function
• Save and reopen Decision, with PMML function
• Save and reopen Decision, with feel function
• Save and reopen Decision, with context