refactor(material-moment-adapter): fix strict property initialization errors

Updates the code to be compatible with strict property initialization.

Author: crisbeto

src/material-moment-adapter/adapter/moment-date-adapter.ts

@@ -65,7 +65,7 @@ export class MomentDateAdapter extends DateAdapter<Moment> {
   // while avoiding mutating the original object passed to us. Just calling `.locale(...)` on the
   // input would mutate the object.
 
-  private _localeData: {
+  private _localeData!: {
     firstDayOfWeek: number;
     longMonths: string[];
     shortMonths: string[];

src/material-moment-adapter/tsconfig.json

@@ -4,6 +4,7 @@
   "compilerOptions": {
     "rootDir": "..",
     "baseUrl": ".",
+    "strictPropertyInitialization": true,
     "paths": {
       "@angular/cdk/*": ["../cdk/*"],
       "@angular/material/*": ["../material/*"],