fix extract names from ThisExpression

[tanhauhau]

Fixes #5033

We assumed object of MemberExpression to be Identifier only, ThisExpression does not have .name, causing .name[0] to be accessing property 0 of undefined

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Tests

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[Conduitry]

Can we get by without making this a js sample test? The reported issue was that the component wouldn't compile at all, which a runtime test would still catch. To test for the correct behavior of the generated code, we could have something like <button on:click={function () {}}> that uses this in some way.