TS 'declare` keyword does not work

[Refzlund]

Describe the bug

declare gets removed from class properties in TypeScript script-tags.

This causes values set from parents to get removed. Ex. if you want to set a value via Object.assign(...)

Reproduction

Svelte Playground

<script module lang='ts'>
	class Parent {
		constructor() {
			this.value = 'Where am I?'
		}
	}

	class Child extends Parent {
		declare value: string
	}
</script>

<script>
	const parent = new Parent()
	const child = new Child()
</script>

<table>
	<tbody>
		<tr><td>Parent</td><td>{parent.value}</td><td>{typeof parent.value}</td></tr>
		<tr><td>Child</td><td>{child.value}</td><td>{typeof child.value}</td></tr>
	</tbody>
</table>

Logs

System Info

System:
    OS: Windows 11 10.0.22631
    CPU: (12) x64 Intel(R) Core(TM) i7-8700K CPU @ 3.70GHz
    Memory: 6.49 GB / 31.93 GB
  Binaries:
    Node: 23.11.0 - C:\Program Files\nodejs\node.EXE
    npm: 10.9.2 - C:\Program Files\nodejs\npm.CMD
    bun: 1.2.16 - ~\.bun\bin\bun.EXE
  Browsers:
    Edge: Chromium (132.0.2957.115)
  npmPackages:
    svelte: ^5.34.1 => 5.34.1

Severity

annoyance