Add new Xperias to various docs

[jovirkku]

This is mostly about adding Xperia 10 IV, Xperia 10 V and Jolla C2 to various documents, and related flashing details. In some cases, I have shortened the sentences in this way: "Xperia XA2 and various Xperia 10 models" or "Xperia XA2 and more recent Xperia models" to avoid long device lists and having to add new models.

The official Sailfish installation instructions for those who install Sailfish to their devices for the first time are kept in the Jolla Shop. They are meant to be clear and straightforward and avoid complicated error handling.

The documents of sailfishos.org (in this commit), in turn, are like an umbrella. They try to describe what one needs to do to reflash Sailfish or what to check if things go wrong. I have added the (missing) direct links pointing to the Shop instructions (even to specific chapters) to make it possible to rely on those original instructions and to avoid rewriting everything in sailfishos.org. In practice, these umbrella docs help the reader pick up only the needed chapters of the Shop instructions when reinstalling Sailfish (e.g., no need to install the drivers again or to unlock the bootloader).

In general, I have shortened the docs wherever there was an opportunity.

One detail: I have replaced "blue LED" with "blue indicator light" because 10 IV and 10 V do not have any physical LEDs but the colourful indicator appears on the display area.

A couple of documents in this commit refer to the Android app stores. As we have just changed them in the Jolla Store, I used the opportunity to update the text in those docs (Aptoide dropped, Aurora added).

[direc85]

Some typos and a few other notices added, but all in all this adds new Xperia devices to documentation, and makes a lot of good improvements here and there.