Added support for string multiplication `str * num`

[lorenzholzbauer]

What type of change does this PR perform?

• [ ] Maintenance (Non-breaking change that updates dependencies)
• [ ] Info or documentation change (Non-breaking change that updates repo info files (e.g. README.md, CONTRIBUTING.md, etc.) or online documentation)
• [ ] Website feature update or docs development changes (Change that changes the design or functionality of the websites or docs)
• [ ] Development or internal changes (These changes do not add new features or fix bugs, but update the code in other ways)
• [ ] Bug fix (Non-breaking change which fixes an issue)
• [x] New feature (Non-breaking change which adds functionality)
• [ ] Breaking change (Major bug fix or feature that would cause existing functionality not to work as expected.)
• [ ] Requires a documentation update, as it changes language or compiler behaviour

Summary

Implemented string multiplication support for multiplicative expressions.

Closes #478

List of Changes

• Implemented support for str * num string multiplication.
• Added new internal function repeatString which is used underneath for the string repetition behaviour.
• Changes multiplication return type behaviour to be equal to the left operand.

Does this PR create new warnings?

None.

Detailed Changelog

Added

• Support for string multiplication using the * operator. (#478).

Linked issues or PRs

• [x] #478

[github-actions[bot]]

size-limit report 📦

Path	Size	Loading time (3g)	Running time (snapdragon)	Total time
./kipper/web/kipper-standalone.min.js	136.2 KB (0%)	2.8 s (0%)	3.2 s (+13.95% 🔺)	5.9 s
./kipper/web/kipper-standalone.js	136.24 KB (0%)	2.8 s (0%)	2.9 s (+13.94% 🔺)	5.6 s

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 78.94737% with 4 lines in your changes missing coverage. Please review.

Project coverage is 83.45%. Comparing base (ff5856d) to head (8bedf39).

:exclamation: Current head 8bedf39 differs from pull request most recent head 444289f

Please upload reports for the commit 444289f to get more accurate results.

Files	Patch %	Lines
kipper/target-js/src/built-in-generator.ts	0.00%	4 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## dev-next #528 +/- ## ============================================ - Coverage 83.49% 83.45% -0.04% ============================================ Files 205 205 Lines 3598 3614 +16 Branches 406 410 +4 ============================================ + Hits 3004 3016 +12 - Misses 421 425 +4 Partials 173 173 ```

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