Enhance Path Resolution for HLSL File Includes

[boobhsi]

This pull request addresses an issue where File.ReadAllText in SetKeywordDeclareType throws a FileNotFoundException when handling .hlsl files that are not specified with an absolute path. This is particularly important for users who utilize relative paths or a special path which consists of Packages and the package name (e.g. Package/com.unity.render-pipelines.universal) to include files in Unity Package Manager.

To enhance flexibility, SetKeywordDeclareType should accommodate file includes specified by absolute paths, relative paths, and package paths.

Changes

• PackagePathResolver: Added a utility class to retrieve the absolute path for a specified package name.

• ReadFromAnyPath: Updated the file reading logic to:

  1. Initially attempt to read the included file using the relative path.
  2. Fallback to reading the file using its absolute path if the relative path fails.
  3. As a final resort, extract the package name and resolve its absolute path using PackagePathResolver, then attempt to read the file.