fix: LEAP-388: Simplify SVG data URL generation

[hlomzik]

encodeSVG() is too complex for expected outcome, so it was simplified.

• No quotes management
• No namespace control (we build that SVG, so have full control already)
• No other unnecessary code we don't need, because SVG is generated by us
• Comments
• Simple unit tests for couple of cases

PR fulfills these requirements

• Tests for the changes have been added/updated
• Docs have been added/updated
• 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

Describe the reason for change

https://github.com/HumanSignal/label-studio-frontend/security/code-scanning/10
Initial idea was to use SVG parser to parse+generate SVG again, but it turned out as a simplier problem

What feature flags were used to cover this change?

None

This change affects (describe how if yes)

• Performance
• Security
• UX

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)

What level of testing was included in the change?

• e2e (codecept)
• integration (cypress)
• unit (jest)

[hlomzik]

Close this PR in favor of monorepo HumanSignal/label-studio#5595