[ffi] CFE/analyzer error messages in different locations.

[dcharkes]

Some of the diagnostics in Dart FFI get reported in different places for CFE vs analyzer. (On a field/class or on the annotation on that field or class.)

• co19/LibTest/ffi/Array/Array.multi_A01_t02
• co19/LibTest/ffi/Array/Array.multi_A02_t01
• co19/LibTest/ffi/Array/Array.multi_A02_t02
• co19/LibTest/ffi/Array/Array_A02_t01
• co19/LibTest/ffi/Array/Array_A02_t02

Some tests rely on the fix in https://dart-review.googlesource.com/c/sdk/+/293600 which has landed today. (So you need the last build of the VM to get the error messages.)

From the triage in:

• Failing FFI tests on CFE sdk#51958