Performance: changes in build paths and typer's application

Motivation and Context

It was reported that Checker project was slow to type with current versions of LIGO after #include was replaced with #import.

Description

In this MR we apply two changes:

• We use Melwyn's observation that paths are not normalized in the build system (and apply his path).
• Then, we optimize application of type-checker to only do work in case there's some case to work (texists_var).
• Finally, it adds an usage of remove_unused for compile expression.

Component

• compiler
• website
• webide
• vscode-plugin
• debugger

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Performance improvement (non-breaking change that improves performance)
• None (change with no changelog)

Changelog

Checklist:

• Changes follow the existing coding style (use dune @fmt to check).
• Tests for the changes have been added (for bug fixes / feature).
• Documentation has been updated.
• Changelog description has been added (if appropriate).
• Start titles under ## Changelog section with #### (if appropriate).
• There is no image or uploaded file in changelog
• Examples in changed behaviour have been added to the changelog (for breaking change / feature).