allow passing schema plugins

[villesau]

Enables passing plugins that work in similar manner to typescript and need to be generated in a single file.

Fixes: #617

Let me know if this is something you'd consider merging and I can work on tests etc. I'm not sure if schemaPlugin is a correct term in this case, but that seemed to be already used in the codebase.

[piglovesyou]

Great. Could you make the build pass? My quick search finds this - Error: Unable to find template plugin matching typescript-urql-graphcache

[villesau]

Sure, I'll fix the remaining tests 👍

[villesau]

@piglovesyou I've now updated the snapshots. is there something needed besides updated snapshots?

I added a mention about the schemaPlugins to the readme. It's a bit funny example since it has both urql and apollo, but I think the idea is the most important idea there.

[villesau]

I would also consider getting rid of this since schemaPlugins allows controlling optional plugins from the outside:

graphql-let/src/lib/codegen.ts

Lines 16 to 27 in 88e9c52

	const OPTIONAL_SCHEMA_PLUGINS = ['typescript-resolvers'];
	function getOptionalSchemaPlugins() {
	const plugins: string[] = [];
	for (const c of OPTIONAL_SCHEMA_PLUGINS) {
	try {
	require(`@graphql-codegen/${c}`);
	plugins.push(c);
	// eslint-disable-next-line no-empty
	} catch (e) {}
	}
	return plugins;
	}

and possibly the default typescript plugin since there's a risk for misconfiguration and having the typescript plugin twice. But those are breaking changes so it does not probably make sense to do such changes in this PR.

[piglovesyou]

Sounds so makes sense. Let's remove OPTIONAL_SCHEMA_PLUGINS (finally!) and ask users to specify typescript-resolvers explicitly. I don't take much time on this project lately, to be honest, so this would be the chance. Or you can leave it if you prefer, it's up to you. In both cases, I'll bump the minor version.

[villesau]

Got rid of OPTIONAL_SCHEMA_PLUGINS and the related logic in the last commit.