`createSourceMapper` incorrectly uses `.toString()` to pass maps to `SourceMapConsumer`

[fabbarix]

Describe the bug
Parsing of source maps fails, this shows up in VSCode as a warning - Unexpected token o in JSON at position 1svelte -
on the first line of Svelte typescript files.

To Reproduce
Setup a project with Svelte and Typescript; open project in VS Code.

Expected behavior
There should be no error.

Screenshots

System (please complete the following information):

• OS: Windows
• IDE: VSCode
• Plugin/Package: svelte-language-server

** Observations **

The issue is in this line of code:

language-tools/packages/language-server/src/plugins/svelte/SvelteDocument.ts

Line 253 in 80828d6

await new SourceMapConsumer(processedSingle.map.toString()),

It uses .toString() to pass the value into the constructor of SourceMapConsumer. This is not needed, and it actually breaks the case where the source map is passed as an object - since the map becomes the string value '[object Object]'.

The source map should be passed as is, since SourceMapConsumer is able to handle both cases - see the _factory method here:

https://github.com/mozilla/source-map/blob/58819f09018d56ef84dc41ba9c93f554e0645169/lib/source-map-consumer.js#L1053

I propose to drop the .toString() - should I create a PR?