refactor: gen unstable flags to avoid conflicts and desync with js

[devsnek]

generate unstable flags from one source to avoid merge conflicts and desync with ids in js

[crowlKats]

maybe call it "unstable flags" or "feature flags" instead of just "flags", to make it less confusing?

[nathanwhit]

should probably add a rerun-if-changed for flags.json

[bartlomieju]

Gonna mark as "request changes" because I'd like to discuss this during the CLI meeting first.

I like that there's a single source of truth in the form of JSON file 👍

[ry]

A refactor to the feature flag system is welcome!

It should encompass all feature flags tho - for example this PR isn't yet handling unstable-lockfile-v5

deno/cli/args/flags.rs

Lines 4462 to 4494 in 9145492

	Arg::new("unstable-sloppy-imports")
	.long("unstable-sloppy-imports")
	.help("Enable unstable resolving of specifiers by extension probing, .js to .ts, and directory probing")
	.env("DENO_UNSTABLE_SLOPPY_IMPORTS")
	.value_parser(FalseyValueParser::new())
	.action(ArgAction::SetTrue)
	.hide(true)
	.long_help(match cfg {
	UnstableArgsConfig::None => None,
	UnstableArgsConfig::ResolutionOnly | UnstableArgsConfig::ResolutionAndRuntime => Some("true")
	})
	.help_heading(UNSTABLE_HEADING)
	.display_order(next_display_order())
	).arg(
	Arg::new("unstable-npm-lazy-caching")
	.long("unstable-npm-lazy-caching")
	.help("Enable unstable lazy caching of npm dependencies, downloading them only as needed (disabled: all npm packages in package.json are installed on startup; enabled: only npm packages that are actually referenced in an import are installed")
	.env("DENO_UNSTABLE_NPM_LAZY_CACHING")
	.value_parser(FalseyValueParser::new())
	.action(ArgAction::SetTrue)
	.hide(true)
	.help_heading(UNSTABLE_HEADING)
	.display_order(next_display_order()),
	).arg(
	Arg::new("unstable-lockfile-v5")
	.long("unstable-lockfile-v5")
	.help("Enable unstable lockfile v5")
	.env("DENO_UNSTABLE_LOCKFILE_V5")
	.value_parser(FalseyValueParser::new())
	.action(ArgAction::SetTrue)
	.help_heading(UNSTABLE_HEADING)
	.hide(true)
	.display_order(next_display_order()),

or fmt-sql

deno/cli/args/mod.rs

Lines 1129 to 1142 in 9145492

	let all_valid_unstable_flags: Vec<&str> = crate::UNSTABLE_GRANULAR_FLAGS
	.iter()
	.map(|granular_flag| granular_flag.name)
	.chain([
	"byonm",
	"bare-node-builtins",
	"detect-cjs",
	"fmt-component",
	"fmt-sql",
	"lazy-dynamic-imports",
	"npm-lazy-caching",
	"npm-patch",
	"sloppy-imports",
	"lockfile-v5",