Implement changes for Combine, Resolve, ofType, README & minor clean-up

[AlexJSully]

Including the following changes:

• Combine method by @AlexJSully
• Resolve method by @vihang-m
• ofType from PR Implement ofType() #20 by @Quarz0
• README fixes from PR Update README.md #21 by @ivorscott
• Clean-up by @AlexJSully & @bitwizeshift

GitOrigin-RevId: 25701006c81810ee439e15793fb746596114c406

[Copilot]

Pull Request Overview

This PR implements new FHIRPath functions (combine, resolve, ofType), adds helper methods for FHIR resources (UnversionedProfileStrings, GetExtensions), updates README examples, and includes various minor clean-ups.

• Introduce UnversionedProfileStrings and GetExtensions helpers with corresponding tests.
• Implement ofType, combine, and resolve FHIRPath functions along with comprehensive tests.
• Update README usage examples to reference fhirpath.Resource and tweak minor comments and workflow scripts.

Reviewed Changes

Copilot reviewed 44 out of 46 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
internal/resource/resource.go	Added UnversionedProfileStrings and GetExtensions methods
internal/resource/resource_test.go	Added tests for UnversionedProfileStrings and extension retrieval
fhirpath/internal/funcs/impl/combine.go	Implemented Combine FHIRPath function
fhirpath/internal/funcs/impl/resolve.go	Implemented Resolve FHIRPath function
fhirpath/internal/funcs/impl/filtering.go	Implemented OfType FHIRPath function
README.md	Updated examples to use fhirpath.Resource
.github/workflows/pr-check.yaml	Expanded PR author sed pattern

Comments suppressed due to low confidence (3)

.github/workflows/pr-check.yaml:38

• The shell test is missing a space before the closing bracket, causing a syntax error. Change it to if [ -z "$body" ]; then.

          if [ -z "$body"]; then

fhirpath/internal/funcs/impl/combine.go:11

• [nitpick] Update the documentation to reflect that the combined collection preserves the order of the input and the provided arguments (deterministic order).

// There is no expectation of order in the resulting collection.

fhirpath/internal/parser/visitor.go:254

• [nitpick] Add a check to ensure v.Functions["ofType"] exists to avoid a panic if the key is missing, e.g. use fn, ok := v.Functions["ofType"]; if !ok { /* error */ }.

	case expr.Inequivalence: