Address PR review comments

- Refactor targetPaths/findOwnPaths to class-based implementations with
  unified caching and .dir/.rootDir properties alongside resolve methods
- Replace jest.mock with jest.spyOn in plugin-manager.test.ts
- Remove paths compatibility wrapper from repo-tools, migrate all internal
  consumers to use targetPaths from @backstage/cli-common directly
- Fix changeset package name (@techdocs/cli not @backstage/techdocs-cli)
- Add migration examples to cli-common changeset
- Update API report for cli-common

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

packages/config-loader/src/sources/ConfigSources.ts

@@ -157,7 +157,7 @@ export class ConfigSources {
   static defaultForTargets(
     options: ConfigSourcesDefaultForTargetsOptions,
   ): ConfigSource {
-    const rootDir = options.rootDir ?? targetPaths.resolveRoot();
+    const rootDir = options.rootDir ?? targetPaths.rootDir;
 
     const argSources = options.targets.map(arg => {
       if (arg.type === 'url') {