fix(api-extractor): suppress private null warning

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot-Session: 8ebd5bf2-c44b-42d5-be25-e7936d4b0a14

Author: bmiddha

apps/api-extractor/src/collector/SourceMapper.ts

@@ -67,6 +67,7 @@ export interface IGetSourceLocationOptions {
 
 export class SourceMapper {
   // Map from .d.ts file path --> ISourceMap if a source map was found, or null if not found
+  // eslint-disable-next-line @rushstack/no-new-null -- The decoupled ESLint plugin does not recognize native private fields yet.
   #sourceMapByFilePath: Map<string, ISourceMap | null> = new Map<string, ISourceMap | null>();
 
   // Cache the FileSystem.exists() result for mapped .ts files