[PBLD-240] Fix for buttons appear disabled with editor light theme (#624)

* use toolbarIcon to set icon dynamically

* fix icon naming

* update changelog

* Update Editor/EditorCore/PolyShapeTool.cs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Update PolyShapeTool.cs

* add unit tests

* implement feedback

* add back iconattribute in polyshape

* implement toolbarIcon for each tool + remove base class

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: zatzuri-unity

CHANGELOG.md

@@ -5,6 +5,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+### Fixed
+
+- [PBLD-240] Fixed a bug where buttons for "Create Cube" and "Create PolyShape" appeared incorrectly on Light theme.
+
 ## [6.0.7] - 2025-08-28
 
 ### Fixed
@@ -33,7 +39,6 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - [PBLD-222] Fixed crash by preventing user from probuilderizing a gameobject that has isPartOfStaticBatch set to true.
 - [PBLD-245] Fixed warnings about obsolete API usage when using Unity 6.2 and later. Updated the API usage where the alternatives were available in Unity 2022.3.
 
-
 ## [6.0.5] - 2025-03-11
 
 ### Changes