Roll ICU to fb520a53

fb520a53 (origin/upstream/master, chromium/master) Add CPEPrefix.
79326efe Make visibility_hidden configuration only pass -fvisibility=hidden on Linux/Android/MacOS
d3f776e0 Add back curr/en_* in android_small
bbf7f88a Append a postfix to the icu target outputs on fuchsia (where target output is hardcoded)
7852ffcb Use filterType: language
8d29692d Allow building icuuc/icui18n with -fvisibility=hidden

This also simplifies the differences introduced in the Fuchsia build
by putting them behind a gn variable, |icu_is_in_fuchsia|.

Bug: 56362
Change-Id: I4b7c7f09b51cdb08f62aaa8a2216d43712b1a025