Greeting text on home screen should be a single TextView

For localization, it’s hard to make sure that the reversed text for each of the two TextViews that comprise the home screen greeting correctly match the flipped layout that Android forms. This is mostly correct today, but it would be more correct if we could combine the strings together. The main challenge has been making sure that:

1. That the line properly extends the whole length of the TextView
2. That when the profile name is really long or display text is large, that the name properly wraps to the next line & the underline is properly resized to not extend past the last character

Another issue with current code is that the screen-reader reads it as Good Morning,, Rajat!. Basically there is one extra ,. This is because the screen-reader adds , between two textviews and we already have one , in text itself.

[rishidyno]

Thanks @rushikeshsuryawanshi.

[rishidyno]

@yashbansal130 In Oppia we follow particular style guide for code formatting and one of the rules in style guide is to not exceed more that 100 char in a line so you will just neet to format the code. Well most of the time all these issues can be fixed automatically while pushing the code but sometimes we have to do it manually. Take refrence from code style guide in wiki.