Note about file path source maps and some cleanup

[captainbrosset]

Rendered articles for review:

• Map the processed code to your original source code, for debugging: https://review.learn.microsoft.com/microsoft-edge/devtools-guide-chromium/javascript/source-maps?branch=pr-en-us-3040 [Public preview] [Before/Live]
• JavaScript debugging features: https://review.learn.microsoft.com/microsoft-edge/devtools-guide-chromium/javascript/reference?branch=pr-en-us-3040 [Public preview] [Before/Live]

This PR adds a short section about a new preference that needs to be enabled when using file path source maps.

The PR also contains some general updating of the source maps article, including moving out the sourceURL section that doesn't have anything to do with the source maps. I moved this section to the reference article instead.

This PR fixes #3019.

AB#48735772

[learn-build-service-prod[bot]]

Learn Build status updates of commit c7d4c3e:

:white_check_mark: Validation status: passed

File	Status	Preview URL	Details
microsoft-edge/devtools-guide-chromium/javascript/reference.md	:white_check_mark:Succeeded	View
microsoft-edge/devtools-guide-chromium/javascript/reference-images/source-url-virtual-names.png	:white_check_mark:Succeeded	View
microsoft-edge/devtools-guide-chromium/javascript/source-maps.md	:white_check_mark:Succeeded	View
microsoft-edge/devtools-guide-chromium/javascript/source-maps-images/close-icon.png	:white_check_mark:Succeeded	View
microsoft-edge/devtools-guide-chromium/javascript/source-maps-images/customize-and-control-devtools-icon.png	:white_check_mark:Succeeded	View

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