Clarify that browsers can use internally-available information about the devices over ideal constraints (#41515)

* Clarify that browsers can use internally-available information about the devices over ideal constraints

Link to specs: https://w3c.github.io/mediacapture-main/

* Fix typo

* Explain user preference in more detail

* Update files/en-us/web/api/mediadevices/getusermedia/index.md

* Update files/en-us/web/api/mediadevices/getusermedia/index.md

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Co-authored-by: Joshua Chen <[email protected]>

Author: ahmedmoussa10

files/en-us/web/api/mediadevices/getusermedia/index.md

@@ -300,6 +300,8 @@ getUserMedia({
 ```
 
 The above will return the camera you requested, or a different camera if that specific camera is no longer available.
+Browsers' internally-available information, such as user preference, may also override your request.
+For example, when the user was asked for camera permissions, the camera they selected may take priority over the one you requested.
 Again, to _require_ the specific camera, you would use:
 
 ```js