feat(select): switch default to AutoPositionStrategy; export IgxSelectOverlapPositionStrategy as opt-in

[Copilot]

igx-select previously defaulted to an internal SelectPositioningStrategy that forced the selected item's text to overlap the input — a tightly-coupled, unexported strategy with no public escape hatch. This changes the default to the standard AutoPositionStrategy (connected to the input, auto-flips when out of viewport) and exposes the previous behavior as an explicit opt-in.

Changes

• New file select-overlap-positioning-strategy.ts — renamed from select-positioning-strategy.ts; class renamed SelectPositioningStrategy → IgxSelectOverlapPositionStrategy

  • Constructor type changed from IgxSelectBase to IgxSelectComponent via import type to avoid a runtime circular import
  • Added ownsScrollPositioning = true marker property so the component can detect the strategy without an instanceof reference

• select.component.ts — default positionStrategy in _overlayDefaults changed to new AutoPositionStrategy(...) with the same PositionSettings defaults (fade animations, Right/Bottom alignment). The instanceof SelectPositioningStrategy guard in onToggleContentAppended replaced with a property-read check (ownsScrollPositioning), removing the value import dependency entirely.

• public_api.ts — exports IgxSelectOverlapPositionStrategy so consumers can construct it directly.

Opt-in to legacy overlap behavior

@ViewChild('select') select: IgxSelectComponent;

ngAfterViewInit() {
  this.select.overlaySettings = {
    positionStrategy: new IgxSelectOverlapPositionStrategy(this.select)
  };
}

Tests

Two new specs added:

• Asserts _overlayDefaults.positionStrategy is an AutoPositionStrategy instance by default
• Asserts assigning IgxSelectOverlapPositionStrategy via overlaySettings is accepted and the dropdown opens/closes correctly