feat: support js/ts config section in VS Code

[jasonlyu123]

fix #2970. This adds support for the new "js/ts" config section in VSCode by merging the modified "js/ts" value into the old format.

Important for non-VSCode users: This doesn't mean allowing the "js/ts" section in the language server. Currently, only "js/ts.hover.maximumLength" is read.

Implementation detail: I was originally going to copy the version for the TypeScript native preview extension. But the version they have now doesn't differentiate js and ts specific config like in the VSCode TypeScript extension.

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Latest commit: 791390c

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