fix: improve contrast of text color

[rros]

Type of change(s)

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

What changed and why

• Updated the contrasting text color selection to chose between Black and White instead of Grey and White.
• Change the way dimming is implemented. Instead of changing the alpha of the background and text colors it keeps the item opaque, but overlays the item with a semi-transparent white box.

Tests performed

Tested the MonthView on both light and dark mode with different background colors.

Before & After preview

Before:

After:

Closes the following issue(s)

• Closes 1.10.3 Locks event text color as dark gray #1065
• Closes Text Contrast on Calender Entry #992

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.

[rros]

Currently only implemented for the MonthView, but should be implemented in every view.