Migrate browser_spec to Jest

What does this MR do?

Migrate browser_spec.js to Jest. Since the original test relies on browser rendering this test was ported as an integration test. In addition, Karma runs this test in a real browser but this test depends on the getBoundingClientRect API which is not available in JSDom (it's available actually but it returns zero for all values) I took the following approach for the migration:

1. I ran all tests in Karma and made notes where it calls getBoundingClientRect with values.
2. I removed all redundant values from these calls
3. I used these values to mock values in JSDom. So basically in current tests we mock initial values after the HTML was set and processed.

Closes #287678 (closed)

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How to setup and validate locally (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
• I have added/updated documentation, or it's not needed. (Is documentation required?)
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• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
• I have tested this MR in all supported browsers, or it's not needed.
• I have informed the Infrastructure department of a default or new setting change per definition of done, or it's not needed.

Security

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• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team