Custom build fails if @text is not included

[sdcooke]

When creating a custom build with the v2.2.5 tag the following happens:

$ python build.py +@dash +@networking +@polyfill
[INFO] Compiling the library...
/Users/sam/Development/open-source/shaka-player/lib/player.js:1996: ERROR - missing require: 'shaka.text.SimpleTextDisplayer'
      return new shaka.text.SimpleTextDisplayer(videoElement);
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

The following works:

python build.py +@dash +@networking +@polyfill +@text

I would have expected @text to be optional.

I started modifying some files to see if it was a quick fix but just hit more code that relied on shaka.text.

[joeyparrish]

Definitely seems like a bug. Any core (required) components related to text should be in the "core" list of sources, not "text".

[joeyparrish]

Fix cherry-picked to v2.2.6.