apacheGH-39722: [JS] Clean up packaging (apache#39723)

* Remove .mts since it's the same as .ts
* Use .js consistently for all packages
* Closes: apache#39722

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Signed-off-by: Matt Topol <zotthewizard@gmail.com>
Co-authored-by: ptaylor <paul.e.taylor@me.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

js/gulp/closure-task.js

@@ -19,7 +19,8 @@ import { targetDir, mainExport, esmRequire, gCCLanguageNames, publicModulePaths,
 
 import fs from 'node:fs';
 import gulp from 'gulp';
-import path from 'node:path';
+import Path from 'node:path';
+import https from 'node:https';
 import { mkdirp } from 'mkdirp';
 import { PassThrough } from 'node:stream';
 import sourcemaps from 'gulp-sourcemaps';