Fixes small error in ActiveRecord::Reflection docs

[ci skip]
Deprecate source_macro

`source_macro` is no longer used in any ActiveRecord code. I've
chosen to deprecate it because it was not marked as nodoc and may
be in use outside of rails source.
rename MiniTest to Minitest
Merge pull request #16373 from eileencodes/deprecate-reflection-source_macro

Deprecate source_macro
Merge pull request #16374 from rajcybage/consistency_minitest

rename MiniTest to Minitest
[ci skip] fix markdown
Merge pull request #16377 from JackDanger/doc-fix-in-association-reflection

Fixes small error in ActiveRecord::Reflection docs
updating documented parameter for build_constraint

Updates documentation in line with changes made in
743b67508e2027e1d086142ccbec47a19fc943f6
Merge pull request #16378 from JackDanger/doc-fix-in-join-association-build_constraint

[doc] updating documented parameter for build_constraint
Add an :if_exists option to drop_table

If set to true, it generates a statement like:

    DROP TABLE IF EXISTS posts

This syntax is supported in the popular SQL servers, that is (at least)
SQLite, PostgreSQL, MySQL, Oracle and MS SQL Sever.