Voice Calculator Added [GSSoC'23] #4159

[Koushik-1729]

I have succesfully deployed this flutter project [ voice calculator ] . PR 4deb0d9

Close #4159 Screenshot of Voice Calculator

Checklist:

• [YES] I have mentioned the issue number in my Pull Request.

• [YES] I have commented my code, particularly in hard-to-understand areas

• [YES] I have created a helpful and easy to understand README.md

• Please add the respective GSSoC labels so that i can get the score

[Koushik-1729]

@MohitGupta121 @pranjay-poddar @TusharKesarwani please take a review of my PR & merge it under GSSOC'23
Thank You !!