TypeSchema/TS: Add choice type narrowing and validation for profiles

[ryukzak]

• Add narrowMergedChoiceDeclarations in flatProfile() to restrict ChoiceFieldDeclaration.choices to only the variants declared by the most derived constraint schema
• Add choiceRestrictions method on TypeSchemaIndex returning Record<string, { permitted, prohibited }> per choice group
• Emit validateExcluded for disallowed choice instances in profile validation

Before (body weight validate() allowed all 11 value[x] variants):

// no validation for valueString, valueBoolean, etc.

After (only valueQuantity permitted, 10 others excluded):

...validateExcluded(res, profileName, "valueCodeableConcept"),
...validateExcluded(res, profileName, "valueString"),
...validateExcluded(res, profileName, "valueBoolean"),
// ... 7 more