feat: add app.getApplicationNameForProtocol API (#20399)

* Add GetApplicationNameForProtocol.

* Fix Windows implementation.

* Fix up test.

* Add documentation.

* Implement for real on Linux using xdg-mime.

Also ensure we allow blocking calls here to avoid errant DCHECKing.

* Improve docs for Linux.

* Clean up tests.

* Add a note about not relying on the precise format.

* Update docs/api/app.md

Co-Authored-By: Shelley Vohr <codebytere@github.com>

* Remove needless `done()`s from tests.

* Use vector list initialization.

* Add a simple test for isDefaultProtocolClient.

* Remove unneeded include and skip a test on Linux CI.

* We no longer differentiate between CI and non-CI test runs.

spec-main/api-app-spec.ts

@@ -846,6 +846,40 @@ describe('app module', () => {
         })
       })
     })
+
+    it('sets the default client such that getApplicationNameForProtocol returns Electron', () => {
+      app.setAsDefaultProtocolClient(protocol)
+      expect(app.getApplicationNameForProtocol(`${protocol}://`)).to.equal('Electron')
+    })
+  })
+
+  describe('getApplicationNameForProtocol()', () => {
+    it('returns application names for common protocols', function () {
+      // We can't expect particular app names here, but these protocols should
+      // at least have _something_ registered. Except on our Linux CI
+      // environment apparently.
+      if (process.platform === 'linux') {
+        this.skip()
+      }
+
+      const protocols = [
+        'http://',
+        'https://'
+      ]
+      protocols.forEach((protocol) => {
+        expect(app.getApplicationNameForProtocol(protocol)).to.not.equal('')
+      })
+    })
+
+    it('returns an empty string for a bogus protocol', () => {
+      expect(app.getApplicationNameForProtocol('bogus-protocol://')).to.equal('')
+    })
+  })
+
+  describe('isDefaultProtocolClient()', () => {
+    it('returns false for a bogus protocol', () => {
+      expect(app.isDefaultProtocolClient('bogus-protocol://')).to.equal(false)
+    })
   })
 
   describe('app launch through uri', () => {