improve docs code blocks highlighting (#2049)

Summary:
This PR adds missing Objective-C entry to the Docusaurus config, fixes Objective-C code blocks label and adds or replaces several code block labels to improve the currently highlighted blocks.

Prism in Docusaurus by default also includes syntax highlight for `jsx` and `tsx`, which improves the nodes and props highlight, so I have used those syntaxes in few places too.

I have also fixed one typo that I have spotted and my IDE made a cleanup of whitespaces in edited files.

## Changelog

* [website] improve docs code blocks highlighting

Pull Request resolved: https://github.com/facebook/flipper/pull/2049

Test Plan:
The changes have been tested running Flipper website on `localhost`.

## Preview

<img width="650" alt="Screenshot 2021-03-12 150934" src="https://user-images.githubusercontent.com/719641/110951135-fff20d00-8344-11eb-96db-1bdc82c8d5ea.png">

<img width="649" alt="Screenshot 2021-03-12 151022" src="https://user-images.githubusercontent.com/719641/110951268-2ca62480-8345-11eb-9d3b-1a48f1267776.png">

Reviewed By: priteshrnandgaonkar

Differential Revision: D27336599

Pulled By: passy

fbshipit-source-id: c2dfb3d8cad4675da0f5e1270cada1e56a0175c0

docs/troubleshooting.mdx

@@ -232,7 +232,7 @@ If you experience errors such as `Undefined symbol: associated type descriptor f
 
 Comment out the relevant lines in `ios/Podfile` and run `cd ios && pod install` again:
 
-```
+```ruby
   # use_flipper!
   # post_install do |installer|
   #  flipper_post_install(installer)
@@ -243,7 +243,7 @@ Comment out the relevant lines in `ios/Podfile` and run `cd ios && pod install`
 
 To speed up CI builds, Flipper can be disabled on CI environments by making the Flipper SDK inclusion conditional (this works on most CI providers, feel free to customize the environment variable):
 
-```
+```ruby
   if !ENV['CI']
     use_flipper!
     post_install do |installer|