[Data Grid]: Fix narrator support for Data Grid tables
[Data Grid]: Fix narrator support for Data Grid tables

Issue:
- Narrator is not properly reading the table accessibility text:
"${this._displayName} ${items}, use the up and down arrow keys to navigate and interact with the rows of the table; Use browse mode to read cell by cell."

Changes:
- Using ARIAUtils.alert instead of _ariaLiveLabel
    - More stable experience while using Narrator

Bug: 1146241
Change-Id: I93dc59080e5f50bfe5e814f476045af4c779c12d
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/2522365
Reviewed-by: Tony Ross <d5807c9a1621d46cc76cd6770054768aff0ae774@microsoft.com>
Reviewed-by: Changhao Han <68542faf32f0a558a873c0f094ca9bedb2744bff@chromium.org>
Commit-Queue: Michael Liao <00d75d81082fdf74688ec453c516b42f7cbf0f40@microsoft.com>

ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend