Refactor test/slow/ext_icu/uspoof.php to split apart the icu_49 components

### HHVM Version

HipHop Repo Compiler 3.20.0-dev (rel)
Compiler: heads/master-0-g24cd87747d9193ea227dc3406d5f3f981eb260e8
Repo schema: 5bc98bb28c29d891e958dea7d119dc42d03e780e

```
hhvm$ ldd ./hphp | grep icu
libicui18n.so.55 => /usr/lib/aarch64-linux-gnu/libicui18n.so.55 (0x0000ffffb2f93000)
libicuuc.so.55 => /usr/lib/aarch64-linux-gnu/libicuuc.so.55 (0x0000ffffb2df5000)
libicudata.so.55 => /usr/lib/aarch64-linux-gnu/libicudata.so.55 (0x0000ffffaffe4000)
```

### Standalone code, or other way to reproduce the problem

```
cp hphp; test/run slow/ext_icu/uspoof.php
```

### Expected result

Test runs cleanly

### Actual result

Test fails because of conditions as described in #3925 , where one of the tests in uspoof depends on ICU 49 semantics. (I am not sure at this writing precisely which line number this test is at.)

### Suggestion

The `ext_icu` directory has some conditional testing already in a subdirectory `icu_49`. Move the offending test into that subdirectory, enabling it to be skipped on newer systems, while preserving the testing on the rest of the ICU tests that are invariant under version.

This is in my brief foray into testing HHVM the last test that fails on aarch64 once the patch at #7912 is applied. It's a minor thing, but it would be a major thing to have the aarch64 CI run clean at least once.