Proper error message added for invalid date format

[PallaviGanorkar]

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

Fixes #1589

Description Clear and concise code change description.

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

Type Choose one: Feature

Screenshots (if applicable)

Checklist

• [x] I have read and acknowledged the Code of conduct.
• [x] I have read the Contributing page.
• [x] I have signed the Google Individual CLA, or I am covered by my company's Corporate CLA.
• [x] I have discussed my proposed solution with code owners in the linked issue(s) and we have agreed upon the general approach.
• [x] I have run ./gradlew spotlessApply and ./gradlew spotlessCheck to check my code follows the style guide of this project.
• [x] I have run ./gradlew check and ./gradlew connectedCheck to test my changes locally.
• [x] 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).

[codecov[bot]]

Codecov Report

Merging #1618 (7a83957) into master (75ac755) will decrease coverage by 1.64%. The diff coverage is 22.85%.

:exclamation: Current head 7a83957 differs from pull request most recent head d30f74b. Consider uploading reports for the commit d30f74b to get more accurate results

@@             Coverage Diff              @@
##             master    #1618      +/-   ##
============================================
- Coverage     36.75%   35.11%   -1.65%     
+ Complexity      330      309      -21     
============================================
  Files           145      145              
  Lines          4859     4844      -15     
  Branches        867      859       -8     
============================================
- Hits           1786     1701      -85     
- Misses         2837     2921      +84     
+ Partials        236      222      -14     

Impacted Files	Coverage Δ
...fhir/datacapture/validation/DateFormatValidator.kt	0.00% <0.00%> (ø)
...e/validation/QuestionnaireResponseItemValidator.kt	0.00% <0.00%> (-100.00%)	:arrow_down:
...hir/datacapture/views/QuestionnaireItemViewItem.kt	42.85% <0.00%> (-1.59%)	:arrow_down:
...uestionnaireItemDateTimePickerViewHolderFactory.kt	56.39% <15.38%> (-2.91%)	:arrow_down:
...ws/QuestionnaireItemDatePickerViewHolderFactory.kt	53.57% <60.00%> (-11.72%)	:arrow_down:
...fhir/datacapture/validation/ConstraintValidator.kt	0.00% <0.00%> (-100.00%)	:arrow_down:
...re/validation/ValueConstraintExtensionValidator.kt	0.00% <0.00%> (-91.67%)	:arrow_down:
...acapture/validation/MaxValueConstraintValidator.kt	0.00% <0.00%> (-75.00%)	:arrow_down:
...acapture/validation/MinValueConstraintValidator.kt	0.00% <0.00%> (-66.67%)	:arrow_down:
... and 8 more

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[PallaviGanorkar]

Handling this issue with different approach in other PR. So closing this PR as its no more required