Added string[] and readonly string[] for NumberFormatProps for defaultValue

[Magofoco]

This PR try to fix a type error of NumberFormatProps when using the MaterialUi Textfield inputComponent in InputProps

Failing example:
https://codesandbox.io/s/wonderful-chaplygin-f3otf
If you go to the component MyInput you can see that the component NumberFormatCustom takes NumberFormatProps as props.
The Material UI Textfied, in its InputProps, can take a inputComponent which can be the NumberFormatCustom component.
This leads to a type error since the props Textfied's defaultValue types are: any (https://material-ui.com/api/text-field/)
while the NumberFormatProps's defaultValue is defined as: string | number | undefined.

I tried to extend the types of defaultValue by including string[] and readonly string[] which seem to solve the above mentioned error

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[s-yadav]

But isn't this wrong.? defaultValue will never be array of string.

[Magofoco]

@s-yadav
I was thinking the same, but apparently it can literally take any.
See several examples here: https://codesandbox.io/s/awesome-benz-7vj06 with different defaultValue types

For example, an array of string such as:
const myArray = ["First Element", "Second Element", "Third"]
if assigned to defaultValue, will produce:
First Element, Second Element, Third Element

[s-yadav]

It can because of typecasting by JS. But that will still be wrong. Also, the type of value and default value should match.
Wrong typing can lead to confusion on dev end.

Is there any other way to force type in material ui.?

I guess the Material-UI has mentioned it as any because the Material UI supports the text field to be rendered as select.

[s-yadav]

Related issue.
#446

From the issue looks like @type/react allows the ReadonlyArray;

@Magofoco Can you also check the suggested solution in that issue.