Internalize CPE generation logic (#2541)

* migrate CPE generation logic to internal

Signed-off-by: Alex Goodman <wagoodman@users.noreply.github.com>

* remove create function

Signed-off-by: Alex Goodman <wagoodman@users.noreply.github.com>

---------

Signed-off-by: Alex Goodman <wagoodman@users.noreply.github.com>

syft/pkg/cataloger/internal/cpegenerate/rpm.go

@@ -0,0 +1,21 @@
+package cpegenerate
+
+import "github.com/anchore/syft/syft/pkg"
+
+func candidateVendorsForRPM(p pkg.Package) fieldCandidateSet {
+	metadata, ok := p.Metadata.(pkg.RpmDBEntry)
+	if !ok {
+		return nil
+	}
+
+	vendors := newFieldCandidateSet()
+
+	if metadata.Vendor != "" {
+		vendors.add(fieldCandidate{
+			value:                 normalizeName(metadata.Vendor),
+			disallowSubSelections: true,
+		})
+	}
+
+	return vendors
+}