Hidden witespaces rules not followed during model save

When a witespace hidden rule is removed and introduced the result of Resource.save is invalid for the grammar.

Example:

Model:
	uses += Use*;

SimpleName hidden():
	ID ('.' ID)*
;

MultiName hidden(WS):
	names += BlockName (',' names += BlockName)*
;

MultiQualifiedName hidden():
	(pre = SimpleName '.')? '{' sub = MultiName '}' ('.' post = BlockName)?
;

BlockName:
	name = SimpleName | MultiQualifiedName
;

Use:
	'use' block = BlockName ';'
;

Simple grammar accepting:

use {
	ieee.{std_logic_1164, numeric_std},
	work
}.all;

But not

use {
	ieee.{std_logic_1164, numeric_std},
	work
} . all;

With spaced in between dots.

If I create a test that generates a new BlockName for a post the output is incoherent:

	// Add to each use a post suffix
	def void addPost(BlockName b, String post) {
		if(b instanceof MultiQualifiedName) {
			if(b.post !== null) {
				b.post.addPost(post);
			} else{
				println('Added new')
				val bn = MyDslFactory.eINSTANCE.createBlockName();
				bn.name = post;
				b.post = bn;
			}
		} else {
			println("Modified: " + b.name)
			b.name = (if(b.name !== null) b.name + '.' else '') + post;
		}
	}
	
	@Test
	def void addonBack() {
		val model = '''
			use {
				ieee.{std_logic_1164, numeric_std},
				work
			};
		'''.parse
		validator.assertNoErrors(model)
		
		// Add implicit '.all' suffix
		model.eResource.allContents.toIterable.filter(Use).forEach[
			it.block.addPost('all');
		]
		
		// Transform back to code
		val sBuff = new ByteArrayOutputStream()
		model.eResource.save(sBuff, #{})
		val sReModel = sBuff.toString
		println(sReModel)
		
		// Validate generated code
		val reModel = sReModel.parse
		validator.assertNoErrors(reModel)
		println(EmfFormatter.objToStr(reModel))
	}

This code fail because the newly added node is rendered as:

use {
	ieee.{std_logic_1164, numeric_std},
	work
} . all;

With extra spaces in a context with hidden()

EDIT: fixed small typos in the example

Reproduce the issue with the supplied grammar and the Resource.save model-mutation test, especially the newly added post node. Inspect how serialization handles hidden whitespace around the inserted dot; done means the saved output reparses without grammar errors and does not introduce the invalid spaces shown in the report.