Support location widget to get current location

[LZRS]

IMPORTANT: All PRs must be linked to an issue (except for extremely trivial and straightforward changes).

Fixes #800

Description
Add a custom component, location-widget in contrib/locationwidget, to detect and pick current location coordinates to populate latitude/longitude questionnaire fields

Alternative(s) considered
Have you considered any alternatives? And if so, why have you chosen the approach in this PR?

Type
Feature

Screenshots (if applicable)

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).

[LZRS]

Questionnaire

{
  "resourceType": "Questionnaire",
  "language": "en",
  "status": "active",
  "date": "2020-11-18T07:24:47.111Z",
  "item": [
    {
      "linkId": "location-widget",
      "type": "group",
      "text": "Location Widget",
      "extension": [
        {
          "url": "https://github.com/google/android-fhir/StructureDefinition/questionnaire-itemControl",
          "valueCodeableConcept": {
            "coding": [
              {
                "system": "https://github.com/google/android-fhir/questionnaire-item-control",
                "code": "location-widget"
              }
            ]
          }
        }
      ],
      "item": [
        {
          "linkId": "latitude",
          "type": "decimal",
          "required": true,
          "text": "Latitude",
          "extension": [
            {
              "url": "gps-coordinate",
              "valueString": "latitude"
            }
          ]
        },
        {
          "linkId": "longitude",
          "type": "decimal",
          "required": true,
          "text": "Longitude",
          "extension": [
            {
              "url": "gps-coordinate",
              "valueString": "longitude"
            }
          ]
        }
      ]
    }
  ]
}

[f-odhiambo]

Can we merge this in ? @jingtang10

[jingtang10]

please feel free to merge once the comments below are addressed.

thanks @LZRS

[jingtang10]

please go through the check list in the pr description @LZRS