Improve performance of function rationalize

[Divyesh-Shah-17]

Describe the bug
The rationalize function is experiencing significant performance issues, causing noticeable slowness. In some cases, this slowness leads to the browser crashing.

To Reproduce
I encountered this issue with a different example, but I found a similar problem in the documentation with the following equation:
math.rationalize('x/(1-x)/(x-2)/(x-3)/(x-4) + 2x/ ( (1-2x)/(2-3x) )/ ((3-4x)/(4-5x) )')

[josdejong]

Thanks for reporting. There may be a clear culprit or some infitite loop occurring there.

Help debugging this issue would be very welcome.

[josdejong]

I've done some debugging, but I do not see an obvious issue causing this performance issue. I think the logic works fine but is just to inefficient to be able to process an expression this complex, making it take forever. I'll move this issue into a discussion about improving the performance.

For reference: there is already a skipped unit test with this example:

mathjs/test/unit-tests/function/algebra/rationalize.test.js

Lines 126 to 131 in d1ecf44

	it.skip('processes a really complex expression', function () {
	// note this test passes but takes for ever to complete
	assert.strictEqual(stri(math.rationalize('x/(1-x)/(x-2)/(x-3)/(x-4) + 2x/ ( (1-2x)/(2-3x) )/ ((3-4x)/(4-5x) )')),
	'(-30*x^7+344*x^6-1506*x^5+3200*x^4-3472*x^3+1846*x^2-381*x)/(-8*x^6+90*x^5-383*x^4+780*x^3-797*x^2+390*x-72)')
	})