chore(web): Replace className with classList and indexOf with includes

Scope of dom/domEventHandlers and dom/domManager

Replace
```
} else if(el?.className?.indexOf('kmw-disabled') >= 0) {
```
with
```suggestion
} else if(el?.classList?.indexOf('kmw-disabled') >= 0) {
```

. And then replace
```
} else if(el?.classList?.indexOf('kmw-disabled') >= 0) {
```
with
```suggestion
} else if(el?.classList?.includes('kmw-disabled')) {
```

Tidier because it's not a substring match and `classList` is [supported](https://caniuse.com/?search=classlist) in all our environments (`includes()` is not, although probably okay because of es6-shim?)

_Originally posted by @mcdurdin in https://github.com/keymanapp/keyman/pull/7662#discussion_r1017457782_

Also investigate to see if this applies to domManager (it has several references to `className.indexOf('kmw-disabled')`