[Feature] Add Base64 paste decoding (Fixes #2317)

[Sl4y3r-07]

Problem description

Ability to paste Base64 with autodetection of base64 when pasting or under the paste as dropdown.

Implementation description

I have added an option Paste all as decoded base64 string under the Paste as option.
I have modified the function pasteBytes() in plugins/builtin/source/content/views/view_hex_editor.cpp and added two functions isValidBase64() and decodeBase64().
It checks if the copied string is empty or its length a multiple of 4 (because a valid base64 string is multiple of 4 or padded with = to satisfy the condition).
Then it decodeBase64 function is called and decoded output is pasted.
For eg, aGVsbG8gd29ybGQ= -> this string is present in my clipboard, I am attaching the screenshot.

Screenshots

[Sl4y3r-07]

@WerWolv Can you please look into it and let me know if further changes are required?