fix(markdown-template): keep parent scope in enum optional blocks

[mttrbrts]

This is a follow-up to #683. @Shubh-Raj raised this case in their review of #647.

#683 keeps the parent scope only when the optional property is primitive. property.isPrimitive() is false for enum fields, so an enum optional still scoped its body to the enum declaration. On main today, all of these fail with Unknown property:

{{#optional billingFrequency}}{{billingFrequency}}{{/optional}}
{{#optional billingFrequency}}{{name}}{{/optional}}
{{#optional billingFrequency}}{{this}}{{/optional}}

Change

OptionalDefinition now treats enum properties as scalars, like primitives:

• the body keeps the parent scope;
• {{this}} resolves to the enum field, as an EnumVariableDefinition with its enumValues.

Tests

The new tests cover:

• named and sibling variables in an enum #optional block;
• rejection of unknown variables;
• {{this}} used together with named variables in the same block, for enum and primitive optionals. @Shubh-Raj also suggested this case.

Results:

• Both new tests fail without the change.
• markdown-template passes (28 tests) and markdown-transform passes (31).
• tsc --noEmit is clean, and ESLint reports no errors.

🤖 Generated with Claude Code

[coveralls]

Coverage Report for CI Build 38133762789

Coverage increased (+0.4%) to 83.247%

Details

• Coverage increased (+0.4%) from the base build.
• Patch coverage: 2 of 2 lines across 1 file are fully covered (100%).
• No coverage regressions found.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

No coverage regressions found.

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Coverage Stats

Relevant Lines:	2412
Covered Lines:	2052
Line Coverage:	85.07%
Relevant Branches:	871
Covered Branches:	681
Branch Coverage:	78.19%
Branches in Coverage %:	Yes
Coverage Strength:	1109.55 hits per line

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💛 - Coveralls