Previously, having a leading or trailing space caused
HTMLElement.classList.add to be called with an empty string (because we
are splitting on whitespace), which is not allowed and caused a crash.
This commit fixes that by trimming the keys of the class object in the
same way that we already do it for class strings.
Before this commit, the generated code crashed if an attribute in
the template contained backticks. The compiler output something
like
```js
let block1 = createBlock(`<div foo="`bar`"/>`);
```
The backticks are now properly escaped.
Samuel Degueldre