Fix package path to reduce nupkg size

[filzrev]

Currently build-in templates don't contains target framework dependent plugin DLLs.
But Microsoft.DocAsCode.App.nupkg contains duplicated content files as below.

/contentFiles/any/net6.0/templates/**
/contentFiles/any/net7.0/templates/**
/contentFiles/any/net8.0/templates/**

This PR set PackagePath as Language- and framework-agnostic
and templates resources are packed to following shared path.

/contentFiles/any/any/templates/**

This PR reduce Microsoft.DocAsCode.App.nupkg package size.
docfx.nupkg package size issue described at #8691 needs additional works.

[filzrev]

CI Tests failed with following error.

Failed! - Failed: 9, Passed: 16, Skipped: 1, Total: 26, Duration: 39 s - docfx.Tests.dll (net7.0)

It seems recent PR tests failed with same issues.

[yufeih]

Does this change breaks the docfx package shipped as a global tool?

[filzrev]

This PR change don't affects docfx.nupkg contents.
(Because docfx reference Microsoft.DocAsCode.App as ProjectReference)
So there is no breaking changes.

---

I though there are 3 execution type to run docfx toolset.

1. Run docfx as .NET global tool (and .NET local tool)
2. Run docfx Self-Contained exe that is published on GitHub Release Page
3. Run custom application that use Microsoft.DocAsCode.App package.

1. and 2. behaviors are guaranteed by there is no output content changes.
And 3. is tested on my local environment. and confirmed no behavior changes.

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: -0.02 ⚠️

Comparison is base (e66d5df) 77.00% compared to head (3c3d0c0) 76.99%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8876      +/-   ##
==========================================
- Coverage   77.00%   76.99%   -0.02%     
==========================================
  Files         605      605              
  Lines       25036    25036              
==========================================
- Hits        19280    19277       -3     
- Misses       5756     5759       +3     

see 2 files with indirect coverage changes

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[yufeih]

Thank you @filzrev, this is a great approach!

[filzrev]

I've confirmed Microsoft.DocAsCode.App 2.67.5 NuGet package size is reduced from 32.14 MB to 10.29 MB.