Replace usage of Maps.newHashMapWithExpectedSize() with standard Java

[HannesWell]

In Java-19 there is even static factory method HashMap.newHashMap(int) that can be used as a drop-in replacement once Java-19 or later is required.
For now I calculate the necessary capacity explicitly using the formula: expected-size *4/3+1.

The change in XtextGeneratorTemplates also removes the usage of Maps.newHashMapWithExpectedSize() of many generated Activators, but I haven't changed them manually. I assume they should be regenerated, shouldn't they?

Part of #2975

[LorenzoBettini]

I think @szarnekow should review this, but personally, I'm not a big fan of such strange expressions for computing the size ;)

another note: Maps.of returns an immutable map, IIRC. Could this potentially lead to breakage if the current factory method returns a mutable list?

[HannesWell]

I think @szarnekow should review this, but personally, I'm not a big fan of such strange expressions for computing the size ;)

Is it about the expression or specifying the size at all?

If it is the latter, I can also remove it. If it is the former I'm fine to restrict this PR to the change of XtextGeneratorTemplates.xtend, which is 'required' for eclipse/mwe#287 (comment) or at least the changes that use only constants. I mainly did the others for completeness.
The remaining parts could then be replaced as soon as Java-21 is required using the method HashMap.newHashMap(int) introduced in Java-19 as mentioned in my initial message.

another note: Maps.of returns an immutable map, IIRC. Could this potentially lead to breakage if the current factory method returns a mutable list?

That's right. But I have only used it in two places where the map is passed as userData to EObjectDescription.create(). And if I have followed the code-path correctly that map is only read there.

[HannesWell]

I have now reverted the changes that require computation of the capacity. That can be replaced once the Java-19 HashMap.newHashMap(int) is available for Xtext.
The main change for this PR in XtextGeneratorTemplates.xtend is not affected by that.