Add support for metals.pantsTargets setting

[murph]

@olafurpg merged basic support for the Pants build tool for metals in scalameta/metals#935

Part of this support is a new user-configurable setting, metals.pantsTargets.

Here's my attempt at adding that setting to the extension settings UI.

I've never touched a vscode extension before, so more than happy for lots of feedback.

[olafurpg]

Thank you for this contribution! The pants integration is still evolving and is unsupported at this time. I think it’s best to wait until it’s stable before adding publicly visible configuration options

[murph]

I understand your caution. Maybe if I added some text indicating that it's experimental and might change?

From the perspective of a beginner wanting to try out this support - the hardest part in getting it working was setting this setting.

[cosmicexplorer]

the hardest part in getting it working was setting this setting.

I'll corroborate that -- I failed multiple times to remember how to do so in demonstrating the pants support to others.

[olafurpg]

It's currently unclear if the pantsTargets setting will stay and it's also unclear what minimum Pants version will be required. I'm actively working on some changes that I'm hoping to have ready in the next couple weeks after which I'm optimistic I'll know better how the final integration will look like.

In the meantime, I would prefer to wait with advertising the Pants integration by making it visible in the VS Code configuration UI. Does that make sense?

[murph]

I can't say I really agree - I don't see the harm in making it easier to configure an early plugin, especially as it only ever matters to users already using Pants for their build.

However, happy to respect your decision here. Thanks for working on this, it has already made me much more productive.