docs(guide/migration): add info for 1.4 (ng)Pattern BC

Breaking change was introduced in commit 0e001084ffff8674efad289d37cb16cc4e46b50a.
This content being included in the migration guide is taken from the commit message of commit 0e001084ffff8674efad289d37cb16cc4e46b50a.

Closes #15758
Closes #15765