fix(tabs): update tab output names

[amcdnl]

Updates the tabs to the following new apis per #6677

• selectChange to selectedTabChange
• onCentering to _onCentering
• onCentered to _onCentered

[josephperrott]

Rather than duplicating the creation of the EventEmitter and then having to call both, why not just have selectedTabChange get the selectChange value currently.

/**
 * Event emitted when the tab selection has changed.
 * @deprecated Use `selectedTabChange` instead.
 */
@Output() get selectChange(): EventEmitter<MdTabChangeEvent> {
  return this.selectedTabChange;
}

/** Event emitted when the tab selection has changed. */
@Output() get selectedTabChange(): EventEmitter<MdTabChangeEvent> = 
  new EventEmitter<MdTabChangeEvent>(true);

Doing it this way, allows for users to move to the new output, and ultimately allows for the removal of the @Output with minimal change to the code in the future as no change is needed below in the file.

[amcdnl]

Thanks for the suggestion. Updated!

[jelbourn]

LGTM

[mmalerba]

@amcdnl your closing mat-tab-body tag looks like it got turned into a md-tab-body tag somehow, mind fixing so I can presubmit?

[amcdnl]

@mmalerba - done :)

[amcdnl]

@andrewseguin - rebased.

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