Fix/603 loop visualization

[henriquelalves]

Please check if the PR fulfills these requirements:

• The commit message follows our guidelines.
• For bug fixes and features:
  • You tested the changes.

Related issue (if applicable): #603

What kind of change does this PR introduce?
This PR adds:

• a "ConsoleHighlighter" node to the RunnableCodeExample, that is used to draw rectangles on selected characters and an Arrow animation on the code.
• a "Step" button as an option to run codes that have "yield()" in them. This allows code examples that simulate running them step-by-step (along with the "ConsoleHighlighter" animations).
• adds some more explanation on Lesson 19 ("Creating arrays") regarding the variable name in the "for" loop, and an "unwrapped" version of the same loop.

Does this PR introduce a breaking change?
Nope.