IgxGrid rendering issues on IE

[rmkrmk]

Description

A lot of IgxGrid samples are not rendered correctly on IE on the staging.

• igniteui-angular version: 7.0.x
• browser: IE

Steps to reproduce

Open staging and try the following IgxGrid samples:
"Row Editing", "Filtering", "Sorting", "Searching", "Export to Excel", "Past from Excel", "Multi Column Headers" and more.

Result

Some of the column headers are missing. The grid content is also missing.

Expected result

The samples should be rendered correctly and should be fully functional.

Attachments

Attach a sample if available, and screenshots, if applicable.

[mpavlinov]

Related: #3047

[HristoP96]

The rendering issues were caused due to not enabling the Autoprefixer plugin to work with grid layouts.

A decision was made that this enabling will be done only on customer side (if they want to use our controls in IE 11).

This pull request provides a documentation on how and why the customers should enable the autoprefixer for grid layout.