Improve maintainability of dotnet-new.IntegrationTests template package version lists

## Improve maintainability of dotnet-new.IntegrationTests template package version lists

### Problem

The `dotnet-new.IntegrationTests` project requires manual updates every time a new .NET version is added or an old version reaches end-of-life. There are three tightly-coupled locations that must be kept in sync:

1. **`PackageReference` items in the `.csproj`** — each supported version of `Microsoft.DotNet.Common.ProjectTemplates` and `Microsoft.DotNet.Web.ProjectTemplates` is listed individually (currently 6.0 through 10.0).
2. **Generated `TemplatePackagesPaths` class** — a code-gen block in the `.csproj` that emits a `const string` for each package's resolved path, also listed individually.
3. **Test code in `SharedHomeDirectory.cs` and `WebProjectsTests.cs`** — each version is installed/referenced by its specific const, requiring a new block of code per version.

When .NET 11.0 ships, at least 10 lines across these three locations need to be added. When a version goes out of support (e.g., 6.0), lines need to be removed. This is error-prone and easy to forget.

### Proposal

Explore using **MSBuild wildcards and item-driven code generation** to eliminate the per-version enumeration:

- **Use wildcard `PackageReference` patterns** (or an MSBuild item group with a version range) so that adding a new version doesn't require editing the `.csproj`. For example, a single parameterized item group that iterates over a list of supported versions defined in one place (e.g., a property like `SupportedTemplateVersions=6.0;7.0;8.0;9.0;10.0`).
- **Generate `TemplatePackagesPaths` dynamically** from the resolved `PackageReference` items using an MSBuild target, rather than hardcoding each const.
- **Replace per-version install calls in test code** (`SharedHomeDirectory.cs`, `WebProjectsTests.cs`) with a loop over an array or collection of paths, so adding a version only requires updating the single source-of-truth property/list.

### Benefits

- Adding or removing a supported .NET version becomes a single-line change in one location.
- Reduces risk of forgetting to update one of the three coupled locations.
- Prevents test compilation/runtime failures from stale version lists.

### Relevant files

- [`test/dotnet-new.IntegrationTests/dotnet-new.IntegrationTests.csproj` (lines 24–57)](https://github.com/dotnet/sdk/blob/main/test/dotnet-new.IntegrationTests/dotnet-new.IntegrationTests.csproj#L24-L57)
- [`test/dotnet-new.IntegrationTests/SharedHomeDirectory.cs`](https://github.com/dotnet/sdk/blob/main/test/dotnet-new.IntegrationTests/SharedHomeDirectory.cs)
- [`test/dotnet-new.IntegrationTests/WebProjectsTests.cs`](https://github.com/dotnet/sdk/blob/main/test/dotnet-new.IntegrationTests/WebProjectsTests.cs)