docs: Fixing typos in Context refdoc

Fixing two issues--a typo ("while-use-use" should be "while-in-use"),
and an open <em> tag that's never closed.

NO_TEST , fixes a doc bug (no code edits).

Staged the fixed doc to:

* go/dac-stage/reference/android/content/Context

Change-Id: Id281128210996bc79cbac73a1304b774ad09cf2f
TEST: [go/abtd docs build + stage]
BUG: 288151309
BUG: 250078085