Update ToPolyline function in BoundedCurve

[KaterynaSloboda]

BACKGROUND:

• ToPolyline() function doesn't work for EllipticalArc

DESCRIPTION:

• This PR fixes the ToPolyline() function inside the BoundedCurve class so that inheriting classes don't get errors. Including EllipticalArc

TESTING:

• Call the new test Elements.Geometry.Tests.EllipticalArcTests.ToPolyline() or call the ToPolyline() method on any class that inherits BoundedCurve

FUTURE WORK:

• Is there any future work needed or anticipated? Does this PR create any obvious technical debt?

REQUIRED:

• [x] All changes are up to date in CHANGELOG.md.

COMMENTS:

• Any other notes.

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This change is 

[DmytroMuravskyi]

Just wanted to leave my 5 cents here that with this change Arc.ToPolyline is redundant as it's 100% same override as base class function.

[KaterynaSloboda]

Just wanted to leave my 5 cents here that with this change Arc.ToPolyline is redundant as it's 100% same override as base class function.

Done