[datetime2] feat(DateInput2): remove target wrapper, fix fill prop

[adidahiya]

Fixes #5472

Checklist

• Includes tests
• Update documentation

Changes proposed in this pull request:

• Refactor DateInput2 to use Popover2's renderTarget API, like we do in Select2, Suggest2, and MultiSelect2. Note that this is a breaking change to the DOM layout, as we have combined the popover target and input group elements into one:

- <span aria-haspopup="true" class="bp4-date-input bp4-popover2-target">
-   <div class="bp4-input-group">
-     <input>
- </span>
+ <div class="bp4-input-group bp4-date-input bp4-popover2-target">
+   <input aria-haspopup="true">
+ </div>

• Fix fill prop so it now works as expected

Reviewers should focus on:

N/A

Screenshot

[blueprint-bot]

fix scss typo

Previews: documentation | landing | table | demo

[blueprint-bot]

fix renderTarget deps, fix tests

Previews: documentation | landing | table | demo

[blueprint-bot]

Fixup comments, remove isOpen dep

Previews: documentation | landing | table | demo