fishgen: Generate short flag custom completions

[Kissaki]

The following starts-with 'complete' where filter covers it as well.

---

Based on PR #1120

---

Example generated file, before and after this set of PRs:

ninja.fish -> ninja.nu

# dry run
extern "ninja" [
	--version					# print ninja version
	...args
]

extern "ninja" [
	-n					# dry run
	-v					# show all command lines while building
	-j					# number of jobs to run in parallel [default derived from CPUs]
	-l					# do not start if load average > N
	-k					# keep going until N jobs fail [default=1]
	-h					# show help
	-d					# enable debugging, specify debug mode
	-w					# adjust warnings, specify flags
	--verbose(-v)					# show all command lines while building
	--version					# print ninja version
	...args
]

gnome-extensions.fish -> gnome-extensions.nu

# 
extern "gnome-extensions" [

	...args
]

# Print help
extern "gnome-extensions help" [

	...args
]

# Print version
extern "gnome-extensions version" [

	...args
]

# Enable extension
extern "gnome-extensions enable" [

	...args
]

# Disable extension
extern "gnome-extensions disable" [

	...args
]

# Reset extension
extern "gnome-extensions reset" [

	...args
]

# Uninstall extension
extern "gnome-extensions uninstall" [

	...args
]

# List extensions
extern "gnome-extensions list" [
	--user					# Show user-installed extensions
	--system					# Show system-installed extensions
	--enabled					# Show enabled extensions
	--disabled					# Show disabled extensions
	--prefs					# Show extensions with preferences
	--updates					# Show extensions with updates
	--details(-d)					# Print extension details
	...args
]

# Show extension info
extern "gnome-extensions info show" [

	...args
]

# Open extension preferences
extern "gnome-extensions prefs" [

	...args
]

# Create extension
extern "gnome-extensions create" [
	--interactive(-i)					# Enter extension information interactively
	...args
]

# Package extension
extern "gnome-extensions pack" [
	--force(-f)					# Overwrite an existing pack
	--out-dir(-o)					# The directory where the pack should be created
	...args
]

# Install extension bundle
extern "gnome-extensions install" [
	--force(-f)					# Overwrite an existing extension
	...args
]

extern "gnome-extensions" [

	...args
]

extern "gnome-extensions help" [

	...args
]

extern "gnome-extensions version" [

	...args
]

extern "gnome-extensions enable" [

	...args
]

extern "gnome-extensions disable" [

	...args
]

extern "gnome-extensions reset" [

	...args
]

extern "gnome-extensions uninstall" [

	...args
]

extern "gnome-extensions list" [
	--user					# Show user-installed extensions
	--system					# Show system-installed extensions
	--enabled					# Show enabled extensions
	--disabled					# Show disabled extensions
	--prefs					# Show extensions with preferences
	--updates					# Show extensions with updates
	--details(-d)					# Print extension details
	...args
]

extern "gnome-extensions info show" [

	...args
]

extern "gnome-extensions prefs" [

	...args
]

extern "gnome-extensions create" [
	--uuid					# The unique identifier of the new extension
	--name					# The user-visible name of the new extension
	--description					# A short description of what the extension does
	--template					# The template to use for the new extension
	--interactive(-i)					# Enter extension information interactively
	...args
]

extern "gnome-extensions pack" [
	--extra-source					# Additional source to include in the bundle
	--schema					# A GSettings schema that should be included
	--podir					# The directory where translations are found
	--gettext-domain					# The gettext domain to use for translations
	--force(-f)					# Overwrite an existing pack
	--out-dir(-o)					# The directory where the pack should be created
	...args
]

extern "gnome-extensions install" [
	--force(-f)					# Overwrite an existing extension
	...args
]

[Kissaki]

Looks like it currently leads to flags being duplicated across commands.

/edit: Was the case before too.

Fix in #1122.