[browser] Add test for OutputType=Library

[maraf]

OutputType=Library has same publish/deployment story as OutputType=Exe.
It will create AppBundle with all necessary JS files.
User has to call dotnet.create() from dotnet.js before getAssemblyExports() is available.
The only difference is that this mode doesn't require Main() method and runMain should fail.

We should cover scenarios from #102806 with automated tests
Also discussed in #109866 (comment)
Check if wasi has enough test coverage

Possible use-cases with browser build (described in #102806 for WASI)

1. "I want to create a plain old .NET library"

• Nothing WASM specific needed
• Output is managed dll
• Can be distributed as nuget package)

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>Library</OutputType>
  </PropertyGroup>
</Project>

2. "I want to create a .NET library with access to browser specific APIs"

• Use standard .NET SDK
• Set RuntimeIdentifier to browser-wasm
• Output is managed dll
• Can be distributed as nuget package)

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>Library</OutputType>
    <RuntimeIdentifier>browser-wasm</RuntimeIdentifier>
  </PropertyGroup>
</Project>

3. "I want to create a .NET application running in browser and have a meaningful main method" (like Blazor does)

• Use Microsoft.NET.Sdk.WebAssembly (or Microsoft.NET.Sdk.BlazorWebAssembly) SDK
• RuntimeIdentifier implicitly set to browser-wasm
• Output is app bundle (dotnet.js, .NET runtime, managed dlls)
• Can be deployed to server

<Project Sdk="Microsoft.NET.Sdk.WebAssembly">
  <PropertyGroup>
    <OutputType>Exe</OutputType>
  </PropertyGroup>
</Project>

4. "I want to create a .NET application running in browser, but my use-case doesn't have a meaningful main method" (I don't have a single entrypoint into my .NET code, but rather want to call JSExports from JavaScript)

• Use Microsoft.NET.Sdk.WebAssembly SDK
• RuntimeIdentifier implicitly set to browser-wasm
• Output is app bundle (dotnet.js, .NET runtime, managed dlls)
• Can be deployed to server, can be wrapped as NPM package

<Project Sdk="Microsoft.NET.Sdk.WebAssembly">
  <PropertyGroup>
    <OutputType>Library</OutputType>
  </PropertyGroup>
</Project>

5. In use-case 4. a situation can occur when two such applications should be hosted on a single page

• a) Each app is built separately and loaded separately (loading 2 .NET runtimes, 2 set of framework dlls trimmed to each needs)
• b) Unifying project is created, the two app projects are referenced and a single app bundle is created and deployed

A.csproj

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>Library</OutputType>
    <RuntimeIdentifier>browser-wasm</RuntimeIdentifier>
  </PropertyGroup>
</Project>

B.csproj

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>Library</OutputType>
    <RuntimeIdentifier>browser-wasm</RuntimeIdentifier>
  </PropertyGroup>
</Project>

App.csproj

<Project Sdk="Microsoft.NET.Sdk.WebAssembly">
  <PropertyGroup>
    <OutputType>Library</OutputType>
  </PropertyGroup>
  <ItemGroup>
    <ProjectReference Include="A.csproj" />
    <ProjectReference Include="B.csproj" />
  </ItemGroup>
</Project>

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[pavelsavara]

My new understanding is that OutputType=Library has same publish/deployment story as OutputType=Exe. It will contain AppBundle with all necessary JS files. The only difference is that it doesn't require Main() method.