feat: print selected build identifiers in preamble before build loop (#2785)

* Initial plan

* Print build identifier list in preamble before build loop

Co-authored-by: henryiii <4616906+henryiii@users.noreply.github.com>

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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: henryiii <4616906+henryiii@users.noreply.github.com>

cibuildwheel/__main__.py

@@ -432,6 +432,10 @@ def print_preamble(platform: str, options: Options, identifiers: Sequence[str])
         msg = "\n".join(error_list)
         raise errors.ConfigurationError(msg)
 
+    n = len(identifiers)
+    print(f"{n} build{'s' if n != 1 else ''} selected:")
+    print(", ".join(identifiers))
+    print()
     print("Here we go!\n")