[antlir] Keep file symbols while stripping debug info

Summary: Preserve FILE symbols required for continuous BOLT profiling.

Test Plan:
```javascript
buck2 test fbcode//antlir/antlir2/features/install/... fbcode//antlir/antlir2/features/extract/...
```

https://www.internalfb.com/intern/testinfra/testrun/10696049244036367

```javascript
objdump --syms usr/local/fbprojects/scribe/bin/scribed | grep " df " | head
0000000000000000 l    df *ABS*  0000000000000000              abi-note.c
```

Size overhead:

```javascript
buck run //scribe/scribed:scribe -- --no-publish --arch x86_64
```

scribed: 476521336 -> 476945312 bytes (+414KB, +0.09%)
rpm: 494418066 -> 494492363 bytes (+72KB, +0.01%)

Reviewed By: vmagro, naveedgol

Differential Revision: D87413300

fbshipit-source-id: 424e9b2af8879abea3803687c64a1ac624893873

Author: aaupov

antlir/antlir2/tools/debuginfo-splitter.py

@@ -75,6 +75,7 @@
     [
         args.objcopy,
         "--strip-debug",
+        "--keep-file-symbols",
         "--remove-section=.pseudo_probe",
         "--remove-section=.pseudo_probe_desc",
         args.binary,