fix: calculate contrast for translucent backgrounds using heuristic to prevent crashes

[rros]

First of all, I'm sorry I introduced a bug with my previous PR.

Type of change(s)

• Bug fix
• Feature / enhancement
• Infrastructure / tooling (CI, build, deps, tests)
• Documentation

What changed and why

The previous PR changed the way the better contrasting color is calculated. However this didn't work for translucent backgrounds. The code would throw an InvalidArgumentException.
This PR fixes that by reverting to a heuristic to calculate the better contrasting color for translucent backgrounds. It uses a similar approach to the old code, but instead of depending on a hard coded threshold for DARK_GREY and WHITE, this code determines a threshold based on the relative luminance of any two colors calculated based on the WCAG standard (https://www.w3.org/WAI/WCAG22/Techniques/general/G17#procedure)

Tests performed

Tested it with the Calendar Widget, which was crashing after the last PR was applied and it did work again after this PR.

Closes the following issue(s)

Checklist

• I read the contribution guidelines.
• I manually tested my changes on device/emulator (if applicable).
• I updated the "Unreleased" section in CHANGELOG.md (if applicable).
• I have self-reviewed my pull request (no typos, formatting errors, etc.).
• I understand every change in this pull request.

[naveensingh]

Thanks.