[system] `CssVarsProvider` should not crash the app if local storage is unavailable

[siriwatknp]

Duplicates

• [X] I have searched the existing issues

Latest version

• [X] I have tested the latest version

Summary 💡

Local storage might not be available in private mode. Pointed out by https://github.com/mui/material-ui/pull/33545#discussion_r938618929.

Reference: https://github.com/mui/mui-x/blob/6be8bcbac5c6df70bf476005383df8731135f573/packages/grid/x-data-grid/src/utils/utils.ts#L13

Examples 🌈

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Motivation 🔦

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