fix(ui5-button): fix icon shrinking (#1258)

Setting smaller width to ui5-button makes its icon shrinking:
Setting flex-shrink: 0, preserves the icon size.

Author: ilhan007

packages/main/src/themes/Button.css

@@ -66,6 +66,7 @@
 	top: -.5rem;
 	position: relative;
 	color: inherit;
+	flex-shrink: 0;
 }
 
 :host([icon-end]) .ui5-button-root {