Allow usage of variable and context in answer expression

[maimoonak]

Fixes #[issue number]

Description
Currently the answer-expression option loading by fhirpath just evaluates the simple version of expression and does not make use of context, variables, and other context data fhirPathEngine.evaluate(questionnaireResponse, expression.expression). This should use ExpressionEvaluator evaluateExpression method with all context data.

Type
Choose one: Feature

Checklist

• I have read and acknowledged the Code of conduct.
• I have read the Contributing page.
• I have signed the Google Individual CLA, or I am covered by my company's Corporate CLA.
• I have discussed my proposed solution with code owners in the linked issue(s) and we have agreed upon the general approach.
• I have run ./gradlew spotlessApply and ./gradlew spotlessCheck to check my code follows the style guide of this project.
• I have run ./gradlew check and ./gradlew connectedCheck to test my changes locally.
• I have built and run the demo app(s) to verify my change fixes the issue and/or does not break the demo app(s).

[santosh-pingle]

@maimoonak
Can you please check on your local machine to see if the build is successful and the unit and Android tests pass as expected?

@omarismail94
I'm not sure, but I'm unable to fetch the detailed log of the Kokoro build failure.
May be not having enough permissions?

[omarismail94]

@maimoonak there is a test that fails:

com.google.android.fhir.datacapture.QuestionnaireViewModelTest > resolveAnswerExpression() should return questionnaire item answer options for answer expression with fhirpath and variable FAILED
    com.google.common.truth.AssertionErrorWithFacts at QuestionnaireViewModelTest.kt:4032

can you fix that?

[jingtang10]

please wait until #2034 is merged. that PR changes the questionnaire view item.

[MJ1998]

I guess these 2 were not needed in this API invocation