Update nuspec to place library under nano TFM

[Copilot]

NuGet packages for nanoFramework libraries must declare a .NETnanoFramework1.0 dependency group and place all library files under lib\netnano1.0 rather than the bare lib folder.

Changes to nanoFramework.System.Threading.nuspec

• Dependency group: Wrapped <dependency> in <group targetFramework=".NETnanoFramework1.0">
• File target path: Changed individual file entries to a single wildcard entry targeting lib\netnano1.0

<dependencies>
  <group targetFramework=".NETnanoFramework1.0">
    <dependency id="nanoFramework.CoreLibrary" version="2.0.0-preview.35" />
  </group>
</dependencies>
...
<file src="nanoFramework.System.Threading\bin\Release\System.Threading.*" target="lib\netnano1.0" />

Follows the pattern established in System.Device.Adc@aab7bca.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Update nuspec to place library under nano TFM</issue_title>
<issue_description>### Details about task
Most of the nuspec files are not using the correct location to place the files.
Files (DLL, PE, PDBX and XML for IntelliSense) should be placed under "lib\netnano1.0" (currently are being placed under "lib" only.
Also they should declare a dependency group for ".NETnanoFramework1.0" target framework.
At the same time those still naming the various file types should use a wildcard instead (e.g. "...\Release\mscorlib.*).
The correct pattern should be (take this nuspec as sample):
nanoframework/System.Device.Adc@aab7bca

Do not change anything else on the nuspec file.

Description

</issue_description>

Comments on the Issue (you are @copilot in this section)

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
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0.0% Coverage on New Code
0.0% Duplication on New Code

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