Add code coverage for monthcalendar

[Zheng-Li01]

related https://github.com/dotnet/winforms/issues/10453

Proposed changes

• Add unit tests for MonthCalendar to test its properties:ShouldSerializeTodayDate, ShouldSerializeAnnuallyBoldedDates ,ShouldSerializeBoldedDates, ShouldSerializeMonthlyBoldedDates, ShouldSerializeMaxDate,ShouldSerializeMinDate, ShouldSerializeTrailingForeColor, ShouldSerializeTitleForeColor, ShouldSerializeTitleBackColor, CanGetDescriptionInternal,
• Add unit tests for MonthCalendar to test its methods: ResetTodayDate, ResetTitleBackColor, ResetTrailingForeColor, ResetTitleForeColor, ResetSelectionRange, ResetMonthlyBoldedDates, ResetMaxDate, ResetCalendarDimensions, ResetAnnuallyBoldedDates, ResetBoldedDates, RaiseMouseClick, DoDefaultAction

• Add unit tests for MonthCalendar to test its events: _onCalendarViewChanged

  Microsoft Reviewers: Open in CodeFlow

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 98.85057% with 2 lines in your changes missing coverage. Please review.

Project coverage is 74.41921%. Comparing base (481bb3d) to head (778df44). Report is 39 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #11519 +/- ## =================================================== + Coverage 74.41264% 74.41921% +0.00657% =================================================== Files 3029 3032 +3 Lines 627892 628370 +478 Branches 46770 46840 +70 =================================================== + Hits 467231 467628 +397 - Misses 157317 157379 +62 - Partials 3344 3363 +19 ``` | [Flag](https://app.codecov.io/gh/dotnet/winforms/pull/11519/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dotnet) | Coverage Δ | | |---|---|---| | [Debug](https://app.codecov.io/gh/dotnet/winforms/pull/11519/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dotnet) | `74.41921% <98.85057%> (+0.00657%)` | :arrow_up: | | [integration](https://app.codecov.io/gh/dotnet/winforms/pull/11519/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dotnet) | `17.98278% <ø> (-0.01465%)` | :arrow_down: | | [production](https://app.codecov.io/gh/dotnet/winforms/pull/11519/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dotnet) | `47.26562% <ø> (+0.02711%)` | :arrow_up: | | [test](https://app.codecov.io/gh/dotnet/winforms/pull/11519/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dotnet) | `96.96763% <98.85057%> (-0.02206%)` | :arrow_down: | | [unit](https://app.codecov.io/gh/dotnet/winforms/pull/11519/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dotnet) | `44.25062% <ø> (+0.05489%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dotnet#carryforward-flags-in-the-pull-request-comment) to find out more.