Add a note about devtools extension tabs order

[captainbrosset]

Fixes #2998.

This PR adds a short note to the end of the Reorder tools section about the fact that tabs added by extensions don't get their order persisted.

Preview: https://review.learn.microsoft.com/en-us/microsoft-edge/devtools-guide-chromium/customize/?branch=pr-en-us-3036#reorder-tools

Live/Before: https://learn.microsoft.com/microsoft-edge/devtools-guide-chromium/customize/#reorder-tools

PR also adds bold globally to "Activity Bar", like was done in incoming paragraph. -mh

AB#48691284

[learn-build-service-prod]

Learn Build status updates of commit 6adb777:

✅ Validation status: passed

File	Status	Preview URL	Details
microsoft-edge/devtools-guide-chromium/about-tools.md	✅Succeeded	View
microsoft-edge/devtools-guide-chromium/accessibility/emulate-vision-deficiencies.md	✅Succeeded	View
microsoft-edge/devtools-guide-chromium/accessibility/lighthouse.md	✅Succeeded	View
microsoft-edge/devtools-guide-chromium/accessibility/test-reduced-ui-motion.md	✅Succeeded	View
microsoft-edge/devtools-guide-chromium/accessibility/test-tab-key-source-order-viewer.md	✅Succeeded	View
microsoft-edge/devtools-guide-chromium/customize/index.md	✅Succeeded	View
microsoft-edge/devtools-guide-chromium/overview.md	✅Succeeded	View
microsoft-edge/devtools-guide-chromium/whats-new/2022/12/devtools-108.md	✅Succeeded	View
microsoft-edge/devtools-guide-chromium/whats-new/2023/02/devtools-110.md	✅Succeeded	View

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