feat/calculator - add calculator functionallity

[nirtamir2]

This PR adds functionality to the calculator as in PuruVJ/macos-web#83.
It also adds tests with jest to the project.

Notice

It is currently implemented more like a windows calculator (which has subtle differences from the macOS calculator).
These functionalities can be implemented in the future (we have tests for the current implementation) but I think it's good enough for now.

Click here to see the differences

• No (math order of operations)[https://en.wikipedia.org/wiki/Order_of_operations]. 1 + 2 * 3 = 7 in macOS but in windows 1 + 2 * 3 is more like 1 + 2 ( = 3 ) , 3 * 3 = 9

it("* before + - math order", () => {
  performPresses([1, "+", 2, "*", 3, "="]);
  expectResultToBe("7"); // this test will return 9 in this PR
});

• Minus for building the numbers can be achieved via the +/- operator instead of -.

it("should allow writing minus as part of the number", () => {
  performPresses(["-", 6]);
  expectResultToBe("-6"); //  actual: 6
});

it("should show minus sign if it's the first key", () => {
  performPresses(["-"]);
  expectResultToBe("-"); // actual: 0
});

it("minus after operator show minus in result", () => {
  performPresses(["*", "-"]);
  expectResultToBe("-"); //  actual: 0
});

• Other edge cases from macOS calculator implementation are not implemented (see this question for example)

Unimplemented small features that can be done separately (UI)

• Add keyboard shortcuts
• Add "blinking" effect to the result after the operator pressed
• Decreasing font size if the result contains "overflow" (I fixed the precision to max 12 digits after dot).
  

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[PuruVJ]

Looks great to me!! Will review tomorrow!

[PuruVJ]

Sorry for the delay. Merged it. Your officially a contributor on macOS web now. Thank you for all your help