[ci skip] ActiveSupport CHANGELOG fixes

[akshay-vishnoi]

1. spacing issues
2. spelling correction
3. grammar correction
4. Add missing docs

refer #16576
cc @chancancode

also check grammar in line 113 and 299

[akshay-vishnoi]

Please check grammar in line 113 and 299.

[rafaelfranca]

I think 113 is wrong, not sure about 299. What you saw wrong there?

[akshay-vishnoi]

it's given part is not clear.

`HashWithIndifferentAccess` better respects `#to_hash` on objects it's given.

[akshay-vishnoi]

Also please suggest correction for 113, i will add them.

[rafaelfranca]

Maybe:

Since ActiveSupport::Notifications only instrument items when there are attached subscriber we don't need to disable instrumentation.

and

HashWithIndifferentAccess better respects #to_hash on objects it receives.