[TASK] Rename API for ApplicationContext

Use the term "applicationContext" instead of "context",
because it is too general and could lead to confusion.

Resolves: #52678
Releases: 6.2
Change-Id: Ib586d9d1eb69e6ca7981ed638d45f7aa5b6e6c70
Reviewed-on: https://review.typo3.org/24541
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn