Merge branch 'mb/diff-default-to-indent-heuristics'

Make the "indent" heuristics the default in "diff" and diff.indentHeuristics
configuration variable an escape hatch for those who do no want it.

* mb/diff-default-to-indent-heuristics:
add--interactive: drop diff.indentHeuristic handling
diff: enable indent heuristic by default
diff: have the diff-* builtins configure diff before initializing revisions
diff: make the indent heuristic part of diff's basic configuration

diff --cc builtin/diff-tree.c
Simple merge

diff --cc diff.c
Simple merge