fix(select): support objects as select values

[kara]

• Please check if the PR fulfills these requirements
• The commit message follows our guidelines: https://github.com/angular/angular/blob/master/CONTRIBUTING.md#commit-message-format
• Tests for the changes have been added (for bug fixes / features)
• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
  This fixes a current bug where objects set as option values and/or [(ngModel)] on select tags are converted to [object Object] strings.
• What is the current behavior?

For the following:

@Component({...})
class MyComp {
   selected: any;
   options: any[] = [
      {name: 'Pepper'},
      {name: 'Salt'},
      {name: 'Paprika'}
   ];

   constructor() {  this.selected = this.options[1]; }
}

<select [(ngModel)]="selected">
   <option *ngFor="#current of options" [value]="current">{{current.name}}</option>
</select>

You might expect the select to display "Salt", but it displays "Pepper" because all option values are set to [object Object]. When selecting new options using the dropdown, the selected property on the component class is set to [object Object].

This PR allows you to write the above code and have the selection updated on both ends as expected.

• Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)
  No breaking changes.

[vsavkin]

could you move it to the constructor?

Since id never changes, it is a bit confusing that you keep resetting it on every value change.

[kara]

@vsavkin All comments should be addressed.

[vsavkin]

Do you mean to use == or ===? Those two things are somewhat distinct in JS, and are very distinct in Dart.

[kara]

I did mean == to fix a Dart error, but thinking about it more, this is a bad solution. Obviously we don't want 6 to match "6". I'll fix it another way.

[vsavkin]

Use looseIdentical

[vsavkin]

I think I can remove this line, and the test will still pass. Can you verify that the selected option is actually Buffalo?

[kara]

@jeffbcross Fixed the Edge issues. Should be ready!

[mary-poppins]

Merging PR #7842 on behalf of @vsavkin to branch presubmit-vsavkin-pr-7842.

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