docs: update installation docs to reflect latest @electron/get changes (#21491)
docs: update installation docs to reflect latest @electron/get changes (#21491)

* doc: update Chinese Electron mirror URL

* doc: replace remaining references of electron-download with @electron/get

* doc: update cache dir example based on recent @electron/get cache changes

bpasero/electron,electron/electron,gerhardberger/electron,electron/electron,seanchas116/electron,bpasero/electron,gerhardberger/electron,bpasero/electron,electron/electron,gerhardberger/electron,seanchas116/electron,bpasero/electron,electron/electron,bpasero/electron,gerhardberger/electron,seanchas116/electron,seanchas116/electron,bpasero/electron,seanchas116/electron,seanchas116/electron,electron/electron,gerhardberger/electron,gerhardberger/electron,electron/electron,bpasero/electron,gerhardberger/electron,electron/electron