[ADF-5311] Extract infinite select scroll loading logic to a reusable component (#6536)

* move translation to core

* select scroll directive

* register directive

* add infinite scroll directive

* clean up component and aditional logic

* use  waitForAsync over async

* update docs

* change output emitter name

* revert to async

* restore default value;

* test

lib/core/directives/infinite-select-scroll.directive.ts

@@ -0,0 +1,66 @@
+/*!
+ * @license
+ * Copyright 2019 Alfresco Software, Ltd.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { Inject, AfterViewInit, Directive, EventEmitter, OnDestroy, Output } from '@angular/core';
+import { MatSelect, SELECT_ITEM_HEIGHT_EM } from '@angular/material/select';
+import { Subject } from 'rxjs';
+import { takeUntil } from 'rxjs/operators';
+
+@Directive({
+    selector: '[adf-infinite-select-scroll]'
+})
+export class InfiniteSelectScrollDirective implements AfterViewInit, OnDestroy {
+    static readonly MAX_ITEMS = 50;
+
+    @Output() scrollEnd = new EventEmitter<Event>();
+
+    private onDestroy$ = new Subject<boolean>();
+    private itemHeightToWaitBeforeLoadNext = 0;
+
+    constructor(@Inject(MatSelect) private matSelect: MatSelect) {}
+
+    ngAfterViewInit() {
+        this.matSelect.openedChange
+            .pipe(takeUntil(this.onDestroy$))
+            .subscribe((opened: boolean) => {
+                if (opened) {
+                    this.itemHeightToWaitBeforeLoadNext = (this.getItemHeight() * (InfiniteSelectScrollDirective.MAX_ITEMS / 2));
+                    this.matSelect.panel.nativeElement.addEventListener('scroll', (event: Event) => this.handleScrollEvent(event));
+                }
+            });
+    }
+
+    ngOnDestroy() {
+        this.onDestroy$.next(true);
+        this.onDestroy$.complete();
+    }
+
+    private handleScrollEvent(event: Event) {
+        if (this.isScrollInNextFetchArea(event)) {
+            this.scrollEnd.emit(event);
+        }
+    }
+
+    private isScrollInNextFetchArea(event: Event): boolean {
+        const target = event.target as HTMLElement;
+        return target.scrollTop >= (target.scrollHeight - target.offsetHeight - this.itemHeightToWaitBeforeLoadNext);
+    }
+
+    private getItemHeight(): number {
+        return parseFloat(getComputedStyle(this.matSelect.panel.nativeElement).fontSize || '0') * SELECT_ITEM_HEIGHT_EM;
+    }
+}