fix: generated id="root{n}" should be removed

[wellwind]

Summary

When using snapshot testing, Angular will generate <div id="root{n}"> root tag every time call TestBed.createComponent; this attribute will cause the snapshot not to be stable and should be removed when serializing content.

Test plan

I have updated the testing snapshot content, fixed the code, and the snapshot testing passed.

Does this PR introduce a breaking change?

• [x] Yes
• [ ] No

All old snapshots containing <div id="root{n}"> will cause failure.

So developers have to update the new snapshot manually after the upgrade.

Other information

[wellwind]

Hi @ahnpnl,

do you think this PR is fine to approve?

[ahnpnl]

Continue in #2565