Add synchronous API for SecureStorage: Get / Set

[scotru]

Description of Change

SecureStorage provides async APIs for getting and setting values: SetAsync/GetAsync. This PR adds a synchronous API on iOS and Android: Set/Get for users who may not want the async wrapping.

Bugs Fixed

None

• Related to issue [Enhancement] Add sync support to SecureStorage #856

API Changes

Added:

• public static string SecureStorage.Get(string key)
• public static void SecureStorage.Set(string key, string value)

Changed:

In some cases, the platform specific async APIs are converted to wrappers around the new synchronous APIs.

Behavioral Changes

Should be fully backwards compatible.

[msftclas]

All CLA requirements met.

[VSC-Service-Account]

Docs Build status updates of commit 3c3fdb7:

✅ Validation status: passed

File	Status	Preview URL	Details
Xamarin.Essentials/SecureStorage/SecureStorage.android.cs	✅Succeeded
Xamarin.Essentials/SecureStorage/SecureStorage.ios.cs	✅Succeeded
Xamarin.Essentials/SecureStorage/SecureStorage.netstandard.cs	✅Succeeded
Xamarin.Essentials/SecureStorage/SecureStorage.shared.cs	✅Succeeded
Xamarin.Essentials/SecureStorage/SecureStorage.uwp.cs	✅Succeeded

For more details, please refer to the build report.

Note: If you changed an existing file name or deleted a file, broken links in other files to the deleted or renamed file are listed only in the full build report.

[VSC-Service-Account]

Docs Build status updates of commit 45a8dbf:

✅ Validation status: passed

File	Status	Preview URL	Details
Xamarin.Essentials/SecureStorage/SecureStorage.android.cs	✅Succeeded
Xamarin.Essentials/SecureStorage/SecureStorage.ios.cs	✅Succeeded
Xamarin.Essentials/SecureStorage/SecureStorage.netstandard.cs	✅Succeeded
Xamarin.Essentials/SecureStorage/SecureStorage.shared.cs	✅Succeeded
Xamarin.Essentials/SecureStorage/SecureStorage.uwp.cs	✅Succeeded

For more details, please refer to the build report.

Note: If you changed an existing file name or deleted a file, broken links in other files to the deleted or renamed file are listed only in the full build report.

[VSC-Service-Account]

Docs Build status updates of commit 37de2c1:

✅ Validation status: passed

File	Status	Preview URL	Details
Xamarin.Essentials/SecureStorage/SecureStorage.android.cs	✅Succeeded
Xamarin.Essentials/SecureStorage/SecureStorage.ios.cs	✅Succeeded
Xamarin.Essentials/SecureStorage/SecureStorage.netstandard.cs	✅Succeeded
Xamarin.Essentials/SecureStorage/SecureStorage.shared.cs	✅Succeeded
Xamarin.Essentials/SecureStorage/SecureStorage.uwp.cs	✅Succeeded

For more details, please refer to the build report.

Note: If you changed an existing file name or deleted a file, broken links in other files to the deleted or renamed file are listed only in the full build report.

[jamesmontemagno]

Thank you so much for the pull request and for opening the issue. Please see my feedback: #856