Improve 'google-ima3' — avoid conflict with the DAI SDK

[AdamWr]

Related issue - AdguardTeam/AdguardFilters#153857
In this case rule like this:

||imasdk.googleapis.com/js/sdkloader/ima3.js$script,redirect=google-ima3,important,domain=mdstrm.com

doesn't work (it breaks video player), because (if I'm not wrong) it overrides some values set by imasdk.googleapis.com/js/sdkloader/ima3_dai.js (google.ima.dai.api).

Maybe we could change this line:

Scriptlets/src/redirects/google-ima3.js

Line 29 in 588a1cf

const ima = {};

to check if window.google.ima is already declared and change it to for example something like this:

const ima = window.google?.ima ? window.google.ima : {};