Updating the Multi-Line InputBlock

[samad-yar-khan]

Idea

• I wanted to add the option in the UiKit where we along with the multiline parameter, we can also specify the size of the input box.

• We can have 3 sizes - small, medium and large.

• A small MultilineInputBlock can have 6 rows(this is the current number of rows). A medium and large input blocks can have 12 and 22 rows respectively.

• Based on the size parameter of block we can conditionally pass the different number of rows to the <TextInputArea> component over here.
  

• This will require changes in both the Apps Engine as well as the UIKit

Why do we need this ?

• In the GitHub App we wanted to add a feature where the user could fetch the code changes of a PR and Review it in Rocket.Chat. I tried Putting the code in a SectionBlock element but all the indentation was gone. Fetching and displaying the code in a MultilineInputBlock not only preserved the indentation but also allowed users to edit the code.
• The problem with the MultilineInput block is that the size is restricted to 6 rows, and its not a pleasant experience to review code on that size of a editor.

• Having a larger input block will enable this us to review code better.
  

• This can also be used for adding a large input block in GitHub App which will allow users to raise new issues from Rocket.Chat channels.

• Our actual intent was to add an editor like Ace as a UiKit component but after watching last weeks community call we realized that would require a lot of planning and would block some of the features we have planned for the GitHub App. But once the main features are developed I would like to plan code editor integration.

[samad-yar-khan]

@ggazzo @MartinSchoeler @tassoevan Can you please look into this idea and let me know if you guys have any suggestions. I look forward to improving this component with you guys :)