[datetime2] feat(DateRangeInput2): remove target wrapper element

[adidahiya]

Changes proposed in this pull request:

Similar to #5473, this PR refactors DateRangeInput2 to use Popover2's renderTarget API, which allows us to flatten the rendered DOM by one level and combine the ControlGroup element w/ the Popover2 target element. Also added .bp4-date-range-input and .bp4-date-range-input-popover classes (surprised they weren't there before in <DateRangeInput>):

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

Reviewers should focus on:

No regressions in behavior (should be covered by test suite)

Screenshot

[blueprint-bot]

[datetime2] feat(DateRangeInput2): remove target wrapper element

Previews: documentation | landing | table | demo

[blueprint-bot]

Add classes

Previews: documentation | landing | table | demo