[ci] Add exe files to API Scan

[pjcollins]

The API Scan job added in commit a10aa38 accidentally excluded some
of our xamarin-android-binutils artifacts. The job has been fixed to
scan the EXE files (and corresponding symbols) that were previously
skipped. The latest scan results appear to be consistent with what was
being reported through VS scans, and we can continue working through
these issues:

1. ApiScan Error missingsymbols - File: aapt2.exe.
Tool: ApiScan: Rule: missingsymbols (Missing Symbols)

2. ApiScan Error documentationnotfound - File: aapt2.exe.
Tool: ApiScan: Rule: documentationnotfound (Documentation Not Found).

3. ApiScan Error improperfileformat - File: as.exe.
Tool: ApiScan: Rule: improperfileformat (Improper File Format).

4. ApiScan Error missingsymbols - File: ld.exe.
Tool: ApiScan: Rule: missingsymbols (Missing Symbols).

5. ApiScan Error improperfileformat - File: libzipsharpnative-3-0.dll.
Tool: ApiScan: Rule: improperfileformat (Improper File Format).

6. ApiScan Error improperfileformat - File: llc.exe.
Tool: ApiScan: Rule: improperfileformat (Improper File Format).

7. ApiScan Error improperfileformat - File: llvm-mc.exe.
Tool: ApiScan: Rule: improperfileformat (Improper File Format).

8. ApiScan Error missingsymbols - File: llvm-strip.exe.
Tool: ApiScan: Rule: missingsymbols (Missing Symbols).