[javascript mode] Support TypeScript this parameter declarations
[javascript mode] Support TypeScript this parameter declarations

Closes #5769

pabloferz/CodeMirror,nightwing/CodeMirror,wingify/CodeMirror,dperetti/CodeMirror,namin/CodeMirror,mtaran-google/CodeMirror,wingify/CodeMirror,SidPresse/CodeMirror,codio/CodeMirror,thomasjm/CodeMirror,hackmdio/CodeMirror,thomasjm/CodeMirror,dperetti/CodeMirror,wingify/CodeMirror,codio/CodeMirror,nightwing/CodeMirror,hackmdio/CodeMirror,notepadqq/CodeMirror,nightwing/CodeMirror,pabloferz/CodeMirror,mtaran-google/CodeMirror,dperetti/CodeMirror,notepadqq/CodeMirror,mtaran-google/CodeMirror,codio/CodeMirror,pabloferz/CodeMirror,hackmdio/CodeMirror,namin/CodeMirror,thomasjm/CodeMirror,SidPresse/CodeMirror,notepadqq/CodeMirror,SidPresse/CodeMirror,namin/CodeMirror