fix: LEAP-762: Fix offsets in domManager for emojis

[Gondragos]

There were some problems with calculating offsets and applying text regions to the text/html containing emojis after domManager was introduced.

• here it might be fixed
• there are new tests for that
• RichText helper for testing is introduces

PR fulfills these requirements

• Commit message(s) and PR title follows the format [fix|feat|ci|chore|doc]: TICKET-ID: Short description of change made ex. fix: DEV-XXXX: Removed inconsistent code usage causing intermittent errors
• Tests for the changes have been added/updated (for bug fixes/features)
• Docs have been added/updated (for bug fixes/features)
• Best efforts were made to ensure docs/code are concise and coherent (checked for spelling/grammatical errors, commented out code, debug logs etc.)
• Self-reviewed and ran all changes on a local instance (for bug fixes/features)

Change has impacts in these area(s)

• Product design
• Backend (Database)
• Backend (API)
• Frontend

What feature flags were used to cover this change?

N/A

Does this PR introduce a breaking change?

• Yes, and covered entirely by feature flag(s)
• Yes, and covered partially by feature flag(s)
• No
• Not sure (briefly explain the situation below)

I hope nobody would like to keep that bug.

What level of testing was included in the change?

• e2e
• integration
• unit

Which logical domain(s) does this change affect?

Text, RichText, HyperText, domManager

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