Change value name for dialog

[AlexandreSajus]

Fixes Avaiga/taipy#382

This is my first PR in GUI, I inferred that this would be the correct change, but please make sure this is functional

[github-actions]

Coverage report for frontend/taipy-gui

Branches coverage not met for global: expected >=80%, but got 62.36178681999115%

St.❔	Category	Percentage	Covered / Total
🟢	Statements	80.63%	2294/2845
🟡	Branches	62.36%	1410/2261
🟡	Functions	74.81%	401/536
🟢	Lines	81.02%	2130/2629

Test suite run success

334 tests passing in 36 suites.

Report generated by 🧪jest coverage report action from 4826c83

[github-actions]

☂️ Python Coverage

current status: ✅

Overall Coverage

Lines	Covered	Coverage	Threshold	Status
5301	4525	85%	85%	🟢

New Files

No new covered files...

Modified Files

No covered modified files...

updated for commit: 4826c83 by action🐍

[FredLL-Avaiga]

• the issue is in the user code
• viselements.json is used for doc and has no impact on the code
• taipy-gui repo is/will soon be archived (changes should go to taipy repo)

[FabienLelaquais]

This is not a good idea.
Backward compatibility has to be maintained as long as we can.
Renaming a property has very little added value (except, and I agree, a better understanding of what it does).
However, when naming Taipy GUI properties, we always need to balance the tradeoff between clearer (and longer) names, and code conciseness.
To me, 'open' is just fine. If 'o' worked, I would have used that.

Bottom line: what's the purpose of that?