feat: Support customizing the modern output via "exports" (#784)

* feat: Support customizing the modern output via "exports" * docs: Adding changeset * refactor: Further support "modern" output name with exports object Co-authored-by: Jason Miller <developit@users.noreply.github.com> * fix: Correcting odd typo Co-authored-by: Jason Miller <developit@users.noreply.github.com>

Author: rschristian

.changeset/tender-pants-film.md

@@ -0,0 +1,5 @@
+---
+'microbundle': patch
+---
+
+Allows users to customize the modern output's filename using "exports" like they can with "esmodules"

src/index.js

@@ -256,6 +256,11 @@ function replaceName(filename, name) {
 );
 }
 
+function walk(exports) {
+if (typeof exports === 'string') return exports;
+return walk(exports['.'] || exports.import || exports.module);
+}
+
 function getMain({ options, entry, format }) {
 const { pkg } = options;
 const pkgMain = options['pkg-main'];
@@ -287,7 +292,10 @@ function getMain({ options, entry, format }) {
 mainNoExtension,
 );
 mainsByFormat.modern = replaceName(
-(pkg.syntax && pkg.syntax.esmodules) || pkg.esmodule || 'x.modern.js',
+(pkg.exports && walk(pkg.exports)) ||
+(pkg.syntax && pkg.syntax.esmodules) ||
+pkg.esmodule ||
+'x.modern.js',
 mainNoExtension,
 );
 mainsByFormat.cjs = replaceName(