Add Fourier Transform feature for CH3 and Built In MIC

[neel1998]

Actual Behaviour
Currently Fourier Transform option is only for CH1 and CH2.

Expected Behaviour
Add Fourier Transform option for CH3 and builtin MIC

Would you like to work on the issue?
Yes

[neel1998]

This one is not yet fixed entirely. Fourier Transform for Built In mic input is still to be implemented. Reopening this issue

[CloudyPadmal]

Don't add tag lines like "Fix #nnn" in PR body. They will automatically closes issues.

Also I got a question. I guess the solution for this issue is something quiet similar to what you've done in #1799 addressing #1798. And this issue is opened for 3 days. Can we get a quick fix for this?

[neel1998]

No actually after converting all capture, audio buffer classes to one, it will be different to have fourier for Built in Mic Audio Input. Still i will make a PR by tonight