DOP-873: Fix sidebar/left navtab on-load flashing

[mango-db]

DOP-873.

The Bug

During the pre-render phase, the window size is undefined. This caused cascading effects in which the showLeftColumn state was false during pre-render. Then, on load, the left column would briefly flash closed before opening. To fix, we add an !isBrowser() check to the logic to ensure that all elements are pre-rendered. During pre-render, the CSS behavior is defined by mongodb-base.css. Post-render, the styles in navigation.module.css now have an additional postRender class such that showNav.postRender and left-column.postRender allow React's toggleLeftColumn() behavior.

Staging

• Staged docs-ecosystem
• Staged docs-node

[sophstad]

Great job! Thanks for the thorough explanation of your work 💯

Would appreciate a brief comment (maybe around line 32) explaining what that code is for.