Add grammar compatibility option to the formatter

[stackoverflow]

No description provided.

[bioball]

Approving to unblock, but, we should figure out what to name this.

Also: we should update the docs.

[bioball]

We shouldn't conflict with the built-in --version flag that already exists.

Names are hard, but, maybe let's call this "grammar version"?

Suggested change

	option(names = arrayOf("-v", "--version"), help = compatVersionHelp)
	option(names = arrayOf("--grammar-version"), help = compatVersionHelp)

I also don't think we need to offer a short version of this flag; descriptive flags help with readability of scripts.

[stackoverflow]

Changed everything to be grammar version and removed the short version. The other good name would be grammar compatibility version, but that's too verbose.

[bioball]

Whatever name we settle on, we should change this and the class name too.

Suggested change

	internal class Builder(sourceText: String, private val version: CompatVersion) {
	internal class Builder(sourceText: String, private val grammarVersion: GrammarVersion) {

[stackoverflow]

Changed.

[bioball]

Move to a shared place, maybe a util.kt or something?

[stackoverflow]

Moved to a utils file.

[bioball]

Two nits:

1. Can we just make this a number? The "V" seems unnecessary.
2. Can we provide a table of grammar version to language version? Something like:

Grammar Version	Pkl Version
1	0.25 - 0.29
2	0.30+

[stackoverflow]

The cli option just requires a number now. I actually just used a number in the beginning but changed it later.
The description for each version is the version span it supports.

--grammar-version=(1|2)    The grammar compatibility version to use.
                           1: 0.25 - 0.29
                           2: 0.30+ (default)