scripted-diff: rename base_blob::data to m_data

Summary:

This is in preparation for exposing a ::data member function.

-BEGIN VERIFY SCRIPT-
sed -i "s/\([^.]\|other.\)data/\1m_data/g" src/uint256.h src/uint256.cpp
-END VERIFY SCRIPT-

Partial backport of core PR19326:
https://github.com/bitcoin/bitcoin/pull/19326/commits/131a2f0337f5c396739a47b60bb856ed84ec8937

The comparison fonction differs due to D1527.

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D9147