Fix callVariant: variant bubble aligning issue

[zhuchcn]

…de merging with their outgoing nodes outside of the variant bubble to avoid complexity exploding

Description

Closes #892

Checklist

• This PR does NOT contain PHI or germline genetic data. A repo may need to be deleted if such data is uploaded. Disclosing PHI is a major problem.
• This PR does NOT contain molecular files, compressed files, output files such as images (e.g. .png, .jpeg), .pdf, .RData, .xlsx, .doc, .ppt, or other non-plain-text files. To automatically exclude such files using a .gitignore file, see here for example.
• I have read the code review guidelines and the code review best practice on GitHub check-list.
• The name of the branch is meaningful and well formatted following the standards, using [AD_username (or 5 letters of AD if AD is too long)]-[brief_description_of_branch].
• I have added the major changes included in this pull request to the CHANGELOG.md under the next release version or unreleased, and updated the date.
• All test cases passed locally.

[zhuchcn]

Fuzz test is good after 14,223 cases.

---------------------------------------------------------
|                  FUZZ TEST SUMMARY                    |
---------------------------------------------------------
|                       pass    fail    none    total   |
| ----------------------------------------------------- |
| snv                   3615    0       0       3615    |
| indel                 3623    0       0       3623    |
| comprehensive         6985    0       0       6985    |
| ----------------------------------------------------- |
| sum                   14223   0       0       14223   |
---------------------------------------------------------