fix: add typescript as valid lang tag

[dummdidumm]

Description

Treat lang="typescript" the same as lang="ts" as the former is valid for Svelte to signal that the script tag contains TS

Additional context

If benefitial for the greater ecosystem, I'm okay with this PR getting rejected as "won't do" and instead persuade people into doing lang="ts" . Right now everyone who transitions to Vite will need to adhere to it, so we could use that as a way to force people to only write lang="ts" from now on.

What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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[bluwy]

Extra context: Svelte (or svelte-preprocess specifically) had always supported lang="typescript", and the usage was 50/50 depending on user preference (Svelte didn't enforce one), so the switch to Vite/SvelteKit had tripped many users in the past. This caveat was also mentioned in vite-plugin-svelte's FAQ.

Although svelte-preprocess also supports type="text/typescript", those are really rare. I don't think Vite needs to support that.

[dummdidumm]

Marked as draft so we can discuss first if this is really beneficial in the long run to have to variants to write this. @dominikg rightfully pointed out that it may be better to force people into one style of signaling that TS is used in the script block.

[dummdidumm]

Closing as we came to agreement it would be better to not add extra stuff and instead standardize around lang="ts"