Add term renderer option for chroma formatter

[williammartin]

Description

This relates to #376

Previously, code blocks were hardcoded to render 8-bit color depth regardless of user preferences. This made it difficult to provide accessible experiences for users who depend upon native terminals' ability to change how base 16 ANSI colors are viewed.

Now, with the functional options pattern, WithChromaFormatter term renderer allows users to choose a different chroma formatter, which allows for selection of one that downsamples colors when rendering code blocks.

Credit @andyfeller who actually wrote this, I'm really just the PR monkey.

[andyfeller]

One other addition in this pull request is WithOptions function, which I want to highlight why we thought it was important to include. Let's look at how this is used and why we think it's important for charmbracelet/glamour

WithOptions

The functional option pattern is useful for gathering options to apply later, however it only allows logic to return a single option.

In the GitHub CLI extension module, extension authors can choose whether to allow markdown to render themes or colors. However the accessible-colors work in cli/go-gh needed to apply multiple options around 1) glamour style and 2) chroma formatter:

// WithTheme is a rendering option that sets the theme to use while rendering the markdown.
// It can be used in conjunction with [term.Theme].
// If the environment variable GLAMOUR_STYLE is set, it will take precedence over the provided theme.
func WithTheme(theme string) glamour.TermRendererOption {
	style := os.Getenv("GLAMOUR_STYLE")
	accessible := accessibility.IsEnabled()
	if style == "" || style == "auto" {
		switch theme {
		case "light", "dark":
			if accessible {
				return glamour.WithOptions(
					glamour.WithStyles(AccessibleStyleConfig(theme)),
					glamour.WithChromaFormatter("terminal16"),
				)
			}
			style = theme
		default:
			style = "notty"
		}
	}
	return glamour.WithStylePath(style)
}

The new WithOptions was based on NewTermRenderer handling of options:

glamour/glamour.go

Lines 66 to 87 in bdc4ec5

	// NewTermRenderer returns a new TermRenderer the given options.
	func NewTermRenderer(options ...TermRendererOption) (*TermRenderer, error) {
	tr := &TermRenderer{
	md: goldmark.New(
	goldmark.WithExtensions(
	extension.GFM,
	extension.DefinitionList,
	),
	goldmark.WithParserOptions(
	parser.WithAutoHeadingID(),
	),
	),
	ansiOptions: ansi.Options{
	WordWrap: defaultWidth,
	ColorProfile: termenv.TrueColor,
	},
	}
	for _, o := range options {
	if err := o(tr); err != nil {
	return nil, err
	}
	}

We thought this could benefit other glamour users in similar situations.

[aymanbagabas]

LGTM