add meterial element index

[최해선 (HSC-1)]

About

#3992
simSetObjectMaterial, simSetObjectMaterialFromTexture function
This feature can be added to other elements when there are multiple elements as shown in the picture below.

How Has This Been Tested?

Screenshots (if appropriate):

When it is a previous function

When the current function is

[Deleted user (ghost)]

All CLA requirements met.

[David Zimmermann (zimmy87)]

Hi 최해선 (@HSC-1), Thank you for submitting this PR! I tested this locally and it works for me, so I'd like to get this merged. However, the failing clang-format check needs to be fixed first. In order to do this, you can either merge the PR I submitted to your fork here: SimtoReal#1, or you can fix the clang-format check manually yourself by performing the following steps:

1. check out your pull request
2. run git checkout master .clang-format in your repo's root folder
3. if you don't have npm installed, download it from https://www.npmjs.com/get-npm
4. run npm install -g clang-format
5. run clang-format -i path/to/file for each failing file (failing files can be found in the details for the clang-format check)
6. run git add -u to track all style changes
7. run git commit -am "apply style from clang-format"
8. run git merge master
9. resolve other non-style conflicts if you have any
10. push changes

Thanks for helping us with these style changes!

[David Zimmermann (zimmy87)]

Hi 최해선 (@HSC-1), looks like the Documentation Build & Deploy / build (pull_request) check is failing due to a syntax error on ln 1578 of client.py in your latest commit here. It looks like you manually applied the clang-format to this file. Right now, our clang-format configuration is only designed for C++, so it can cause errors like this in python. Can you revert the changes to client.py in your latest commit?

[David Zimmermann (zimmy87)]

There are some remaining artifacts from the edits to client.py that we'd like to see removed before merging.

[David Zimmermann (zimmy87)]

Thanks for submitting this PR 최해선 (@HSC-1)! The AirSimCI Ubuntu_1804 check is failing due an issue with a CUDA repository unrelated to this fix (we're currently working on fixing this issue in a separate PR), so I am moving ahead with merging this.