Add value to md-dialog-close attribute

[NCC1701M]

Feature request

What is the expected behavior?

It should be possible to assign a value to the md-dialog-close attribute which will be next value of the afterClose observable. For example:

<md-dialog-actions align="end">
	<button md-raised-button [md-dialog-close]="'ABC'">No</button>
	<button md-raised-button [md-dialog-close]="'DEF'" color="primary">Yes</button>
</md-dialog-actions>

const dlgRef = this._dialog.open(ConfirmationDialogComponent);
dlgRef.afterClosed().subscribe(next => {
   if (next === "ABC") {
      this.doThis();
   } else {
      this.doThat();
   }
});

or

<md-dialog-actions align="end">
	<button md-raised-button [md-dialog-close]="false">No</button>
	<button md-raised-button [md-dialog-close]="true" color="primary">Yes</button>
</md-dialog-actions>

const dlgRef = this._dialog.open(ConfirmationDialogComponent);
dlgRef.afterClosed().subscribe(next => {
   if (next) {
      this.doThis();
   } else {
      this.doThat();
   }
});

What is the current behavior?

md-dialog-close closes the dialog but doesn't pass a value.

What is the use-case or motivation for changing an existing behavior?

To simplify the implementation of a md-dialog component.

Which versions of Angular, Material, OS, browsers are affected?

Component	Version
@angular/cli	1.0.2
node	7.10.0
os	win32 x64
browsers	all
@angular/animations	4.1.1
@angular/common	4.1.1
@angular/compiler	4.1.1
@angular/core	4.1.1
@angular/forms	4.1.1
@angular/http	4.1.1
@angular/material	2.0.0-beta.3
@angular/platform-browser	4.1.1
@angular/platform-browser-dynamic	4.1.1
@angular/platform-server	4.1.1
@angular/router	4.1.1
@angular/cli	1.0.2
@angular/compiler-cli	4.1.1

[devversion]

Done with #4332

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