Replace the activationEvent "*" with "onStartupFinished"

[whitphx]

The Start up ("*") activation point is generally not preferred and onStartupFinished is referred to as a better alternative.

For example, another keybindings extension vscode-sublime-keybindings has switched its activation point from * to onStartupFinished: microsoft/vscode-sublime-keybindings#158
Also, some built-in extensions have fixed this as well (, while some haven't with explicit decision to opt-in the "*"): microsoft/vscode#110031
The VsCodeVim extension follows this as well (VSCodeVim/Vim#8548)

For the version compatibility, onStartupFinished has been available since 1.46.0, so this change doesn't have a negative side effect on the supported version of this extension:

vscode-emacs-mcx/package.json

Lines 11 to 13 in 04182e2

	"engines": {
	"vscode": "^1.63.0"
	},