fix(ivy): multi provider override support in TestBed

[AndrewKushnir]

Overriding multi provider values (providers with multi: true flag) via TestBed require additional handling: all existing multi-provider values for the same token should be removed from the override list, so that they are not included into the final value of a given provider. This commit adds this logic to make sure we handle multi providers correctly.

This PR resolves FW-1251.

PR Type

What kind of change does this PR introduce?

• Bugfix

Does this PR introduce a breaking change?

• Yes
• No

[kara]

LGTM

[kara]

presubmit

[ngbot]

I see that you just added the PR action: merge label, but the following checks are still failing:
     status "ci/circleci: integration_test" is failing
     missing required status "ci/circleci: publish_snapshot"

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[kara]

merge-assistance: integration test for size broken on master

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