Improve semicolon delimiter consistency, fix IsNetstandard property

[Arlodotexe]

This pull request includes minor changes to the target framework properties and the UseTargetFrameworks script to ensure consistency by adding semicolons at the end of framework lists.

Changes to target framework properties:

• MultiTarget/AvailableTargetFrameworks.props: Added a semicolon at the end of the DotnetStandardCommonTargetFramework property value.
• MultiTarget/EnabledMultiTargets.props: Added a semicolon at the end of the EnabledMultiTargets property value.

Changes to UseTargetFrameworks script:

• MultiTarget/UseTargetFrameworks.ps1: Modified the regex replacement to include a semicolon at the end of the EnabledMultiTargets property value.

The delimiter is needed to avoid problems with the Contains checks between TFMs such as net9.0 and net9.0-windows*.