Don't offer to show lifted-core IR when it doesn't exist

[jiribenes]

We shouldn't offer to print lifted-core IR for versions where it doesn't exist. (≥0.4.0)
If it can't be conditional [?], then we should either produce a warning when it's selected with an old version or just remove the option altogether.

effekt-vscode/package.json

Lines 113 to 131 in e3879ce

	"effekt.showIR": {
	"type": "string",
	"default": "none",
	"enum": [
	"none",
	"source",
	"core",
	"lifted-core",
	"machine",
	"target"
	],
	"enumDescriptions": [
	"Disable showing intermediate representation.",
	"Show source tree after parsing.",
	"Show the core intermediate representation after capability-passing transformation.",
	"Show the core intermediate representation after lift inference.",
	"Show the machine representation.",
	"Show the generated code in the target language."
	]