[docs][data grid] Audit and revise the Pro column docs

[mapache-salvaje]

Part of the ongoing auditing/editing project, prioritizing Pro and Premium features.

Pages audited: Column ordering, Column pinning

• changes "Column ordering" to "Drag-and-drop column reordering"
• adds more structure to the pages via informative headers
• implements style guide and best practices

[mui-bot]

Deploy preview: https://deploy-preview-17844--material-ui-x.netlify.app/

Updated pages:

• docs/data/data-grid/column-ordering/column-ordering.md
• docs/data/data-grid/column-pinning/column-pinning.md
• docs/data/data-grid/column-spanning/column-spanning.md

Bundle size report

Total Size Change: 0B^(0.00%) - Total Gzip Change: 0B^(0.00%) Files: 120 total (0 added, 0 removed, 0 changed)

Details of bundle changes

Generated by :no_entry_sign: dangerJS against 0e83b9867204e7d2d50967aff68eb5926269cb12

[github-actions[bot]]

This pull request has conflicts, please resolve those before we can evaluate the pull request.

[github-actions[bot]]

Cherry-pick PRs will be created targeting branches: v7.x