fix: decode URL-encoded characters

[neutiyoo]

Description

This PR fixes the URL decoding issue with base64 encoded contract codes.

For example, bWFwcGluZyhhZGRyZXNzID0+IHVpbnQyNTYpIHB1YmxpYyBmb287 is base64 encoded value of mapping(address => uint256) public foo;.

+ is URL encoded to %2B causing the following error in the Remix IDE:

DOMException: Failed to execute 'atob' on 'Window': The string to be decoded is not correctly encoded.

The decodeURIComponent function is used to decode any URL-encoded characters in the params.code string before passing it to the atob function. This is necessary because atob expects a string that has already been encoded in base64 format and does not handle URL-encoded characters. By applying decodeURIComponent first, you ensure that the atob function will be able to properly decode the base64-encoded string.

NOTE:
The set of characters used in Base64 encoding includes the 26 uppercase letters of the alphabet (A-Z), the 26 lowercase letters (a-z), the 10 digits (0-9), and two additional characters: the plus sign (+) and the forward slash (/). Additionally, the equals sign (=) is used as a padding character to make the length of the output a multiple of 4.

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