[Ionic 4.5.0] ion-button lost background focused & activated Custom Properties colors

# Bug Report

**Ionic version:**

[x] **4.5.0**

Ionic/angular - focused and activated button states now always show `--ion-color-primary` regardless of the button css properties.

Adding `fill="clear"` adds transparency but still not using the `--background-focused` of the css (this trick used to work in the past)

**Ionic info:**

Ionic CLI : 5.0.1 (C:\Users\jo\AppData\Roaming\npm\node_modules\ionic)
Ionic Framework : @ionic/angular 4.5.0
@angular-devkit/build-angular : 0.13.9
@angular-devkit/schematics : 7.3.9
@angular/cli : 7.3.9
@ionic/angular-toolkit : 1.5.1

Utility:

cordova-res : 0.3.0
native-run : 0.2.4

System:

NodeJS : v10.15.3 (F:\Program Files\nodejs\node.exe)
npm : 6.4.1
OS : Windows 10

Reproduce the issue with Ionic 4.5.0 using an ion-button and custom color properties, including the fill="clear" case. Start by tracing the ion-button component styles and verify that focused and activated states honor --background-focused and the configured color rather than always using --ion-color-primary.

由索引模型根据 Issue 内容生成。