refactor(material/table): fix strict property initialization errors

Updates the code to be compatible with strict property initialization.

Author: crisbeto

src/material/table/table-data-source.spec.ts

@@ -88,5 +88,5 @@ describe('MatTableDataSource', () => {
   imports: [MatSortModule],
 })
 class MatSortApp {
-  @ViewChild(MatSort, {static: true}) sort: MatSort;
+  @ViewChild(MatSort, {static: true}) sort!: MatSort;
 }

src/material/table/table-data-source.ts

@@ -69,7 +69,7 @@ export class MatTableDataSource<
    * For example, a 'selectAll()' function would likely want to select the set of filtered data
    * shown to the user rather than all the data.
    */
-  filteredData: T[];
+  filteredData!: T[];
 
   /** Array of data that should be rendered by the table, where each object represents one row. */
   get data() {

src/material/table/table.spec.ts

@@ -698,7 +698,7 @@ class MatTableApp {
   columnsToRender = ['column_a', 'column_b', 'column_c'];
   isFourthRow = (i: number, _rowData: TestData) => i == 3;
 
-  @ViewChild(MatTable) table: MatTable<TestData>;
+  @ViewChild(MatTable) table!: MatTable<TestData>;
 }
 
 @Component({
@@ -732,7 +732,7 @@ class NativeHtmlTableApp {
   dataSource = new FakeDataSource();
   columnsToRender = ['column_a', 'column_b', 'column_c'];
 
-  @ViewChild(MatTable) table: MatTable<TestData>;
+  @ViewChild(MatTable) table!: MatTable<TestData>;
 }
 
 @Component({
@@ -805,7 +805,7 @@ class StickyTableApp {
   dataSource = new FakeDataSource();
   columnsToRender = ['column_a'];
 
-  @ViewChild(MatTable) table: MatTable<TestData>;
+  @ViewChild(MatTable) table!: MatTable<TestData>;
 }
 
 @Component({
@@ -834,7 +834,7 @@ class MatTableWithWhenRowApp {
   dataSource = new FakeDataSource();
   isFourthRow = (i: number, _rowData: TestData) => i == 3;
 
-  @ViewChild(MatTable) table: MatTable<TestData>;
+  @ViewChild(MatTable) table!: MatTable<TestData>;
 }
 
 @Component({
@@ -872,10 +872,10 @@ class ArrayDataSourceMatTableApp implements AfterViewInit {
   dataSource = new MatTableDataSource<TestData>();
   columnsToRender = ['column_a', 'column_b', 'column_c'];
 
-  @ViewChild(MatTable) table: MatTable<TestData>;
-  @ViewChild(MatPaginator) paginator: MatPaginator;
-  @ViewChild(MatSort) sort: MatSort;
-  @ViewChild(MatSortHeader) sortHeader: MatSortHeader;
+  @ViewChild(MatTable) table!: MatTable<TestData>;
+  @ViewChild(MatPaginator) paginator!: MatPaginator;
+  @ViewChild(MatSort) sort!: MatSort;
+  @ViewChild(MatSortHeader) sortHeader!: MatSortHeader;
 
   constructor() {
     this.underlyingDataSource.data = [];
@@ -925,8 +925,8 @@ class MatTableWithSortApp implements OnInit {
   dataSource = new MatTableDataSource<TestData>();
   columnsToRender = ['column_a', 'column_b', 'column_c'];
 
-  @ViewChild(MatTable) table: MatTable<TestData>;
-  @ViewChild(MatSort) sort: MatSort;
+  @ViewChild(MatTable) table!: MatTable<TestData>;
+  @ViewChild(MatSort) sort!: MatSort;
 
   constructor() {
     this.underlyingDataSource.data = [];
@@ -977,8 +977,8 @@ class MatTableWithPaginatorApp implements OnInit {
   dataSource = new MatTableDataSource<TestData>();
   columnsToRender = ['column_a', 'column_b', 'column_c'];
 
-  @ViewChild(MatTable) table: MatTable<TestData>;
-  @ViewChild(MatPaginator) paginator: MatPaginator;
+  @ViewChild(MatTable) table!: MatTable<TestData>;
+  @ViewChild(MatPaginator) paginator!: MatPaginator;
 
   constructor() {
     this.underlyingDataSource.data = [];
@@ -1055,7 +1055,7 @@ class TableWithNgContainerRow {
 class MatFlexTableApp {
   dataSource = new FakeDataSource();
   columnsToRender = ['column_a', 'column_b', 'column_c'];
-  @ViewChild(MatTable) table: MatTable<TestData>;
+  @ViewChild(MatTable) table!: MatTable<TestData>;
 }
 
 function getElements(element: Element, query: string): Element[] {