Make showing the URL for a method work for code not hosted on Github

[oxinabox]

The code that finds the URL for the source for a method doesn't work for code that is not hosted on GitHub.
We should make it work for other major providers at least,
like gitlab and bitbucket.

julia/base/methodshow.jl

Lines 200 to 238 in f4c7779

	function url(m::Method)
	M = m.module
	(m.file == :null || m.file == :string) && return ""
	file = string(m.file)
	line = m.line
	line <= 0 || occursin(r"In\[[0-9]+\]", file) && return ""
	Sys.iswindows() && (file = replace(file, '\\' => '/'))
	libgit2_id = PkgId(UUID((0x76f85450_5226_5b5a,0x8eaa_529ad045b433)), "LibGit2")
	if inbase(M)
	if isempty(Base.GIT_VERSION_INFO.commit)
	# this url will only work if we're on a tagged release
	return "https://github.com/JuliaLang/julia/tree/v$VERSION/base/$file#L$line"
	else
	return "https://github.com/JuliaLang/julia/tree/$(Base.GIT_VERSION_INFO.commit)/base/$file#L$line"
	end
	elseif root_module_exists(libgit2_id)
	LibGit2 = root_module(libgit2_id)
	try
	d = dirname(file)
	return LibGit2.with(LibGit2.GitRepoExt(d)) do repo
	LibGit2.with(LibGit2.GitConfig(repo)) do cfg
	u = LibGit2.get(cfg, "remote.origin.url", "")
	u = match(LibGit2.GITHUB_REGEX,u).captures[1]
	commit = string(LibGit2.head_oid(repo))
	root = LibGit2.path(repo)
	if startswith(file, root) || startswith(realpath(file), root)
	"https://github.com/$u/tree/$commit/"*file[length(root)+1:end]*"#L$line"
	else
	fileurl(file)
	end
	end
	end
	catch
	return fileurl(file)
	end
	else
	return fileurl(file)
	end
	end

The fix isn't too hard,
LibGit2 already contains a Regex that parses URLs.
And so one just needs to use that, to get the hostname rather than hard-coding to Github.
GitLab at least uses that exact same URL pattern as Github,
in terms of

https://$(host)/$(user)/tree/$(branch)/$(path)#L$(line)"

Cross-ref: #30139

[oxinabox]

CF: JuliaLang/Pkg.jl#960