Unexport types and functions cataloger packages (#2530)

* unexport as many types and functions from cataloger packages as possible

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

* capture type and signature information in convention test

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

* check that we return pkg.Cataloger from constructors

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

---------

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

syft/pkg/cataloger/java/parse_gradle_lockfile.go

@@ -13,8 +13,8 @@ import (
 
 const gradleLockfileGlob = "**/gradle.lockfile*"
 
-// LockfileDependency represents a single dependency in the gradle.lockfile file
-type LockfileDependency struct {
+// lockfileDependency represents a single dependency in the gradle.lockfile file
+type lockfileDependency struct {
 	Group   string
 	Name    string
 	Version string
@@ -27,7 +27,7 @@ func parseGradleLockfile(_ context.Context, _ file.Resolver, _ *generic.Environm
 	scanner := bufio.NewScanner(reader)
 
 	// Create slices to hold the dependencies and plugins
-	dependencies := []LockfileDependency{}
+	dependencies := []lockfileDependency{}
 
 	// Loop over all lines in the file
 	for scanner.Scan() {
@@ -43,7 +43,7 @@ func parseGradleLockfile(_ context.Context, _ file.Resolver, _ *generic.Environm
 		// we have a version directly specified
 		if len(parts) == 3 {
 			// Create a new Dependency struct and add it to the dependencies slice
-			dep := LockfileDependency{Group: parts[0], Name: parts[1], Version: parts[2]}
+			dep := lockfileDependency{Group: parts[0], Name: parts[1], Version: parts[2]}
 			dependencies = append(dependencies, dep)
 		}
 	}