Currently the `template-var-assignment` migration incorrectly warns if
the template writes to a property in the component that has the same
`ast.PropertyWrite´ name as a template input variable but different
receiver. e.g.
```html
<!-- "someProp.element" will be incorrectly reported as template variable assignment -->
<button *ngFor="let element of list" (click)="someProp.element = null">Reset</button>
```
Similarly if an output writes to a component property with the same name as a
template input variable, but the expression is within a different template scope,
the schematic currently incorrectly warns. e.g.
```html
<button *ngFor="let element of list">{{element}}</button>
<!-- The "element = null" expression does not refer to the "element" template input variable -->
<button (click)="element = null"></button>
```
PR Close#30026
Introduces a new update schematic called "template-var-assignment"
that is responsible for analyzing template files in order to warn
developers if template variables are assigned to values.
The schematic also comes with a driver for `tslint` so that the
check can be used wtihin Google.
PR Close#29608
Paul Gschwendtner