refactor: rename MDC strong-focus indicator mixin for consistent naming

* refactor: rename MDC strong-focus indicator mixin for consistent naming

Recently we renamed all MDC-based mixins from a `-mdc` suffix to
the `mat-mdc` prefix. This didn't happen for the MDC focus indicator
theme which has been added to the `density-api` WIP branch (to account
for the new theming API). To ensure that mixins are all consistent, the
mixin name should be updated to the `mat-mdc` prefix.

* fix: focus-indicator theme mixin should not throw if color is passed

c522351 that landed in the density WIP
branch created theme mixins for the strong-focus indicators. It looks
like logic for supporting an actual color to be specified is currently
broken as we still try to extract the color config from a color
variable.

Author: devversion

src/dev-app/theme.scss

@@ -23,7 +23,7 @@
 // Include base styles for strong focus indicators.
 .demo-strong-focus {
   @include mat-strong-focus-indicators();
-  @include mat-strong-focus-indicators-mdc();
+  @include mat-mdc-strong-focus-indicators();
 }
 
 // Define the default theme (same as the example above).
@@ -57,7 +57,7 @@ $dark-theme: mat-dark-theme((
 // Include the default theme for focus indicators.
 .demo-strong-focus {
   @include mat-strong-focus-indicators-theme($candy-app-theme);
-  @include mat-strong-focus-indicators-theme-mdc($candy-app-theme);
+  @include mat-mdc-strong-focus-indicators-theme($candy-app-theme);
 }
 
 // Include the alternative theme styles inside of a block with a CSS class. You can make this
@@ -74,7 +74,7 @@ $dark-theme: mat-dark-theme((
 // Include the dark theme for focus indicators.
 .demo-unicorn-dark-theme.demo-strong-focus {
   @include mat-strong-focus-indicators-theme($dark-theme);
-  @include mat-strong-focus-indicators-theme-mdc($dark-theme);
+  @include mat-mdc-strong-focus-indicators-theme($dark-theme);
 }
 
 // Create classes for all density scales which are supported by all MDC-based components.

src/material-experimental/mdc-helpers/_focus-indicator.scss

@@ -1,6 +1,6 @@
 @import '../../material/core/theming/theming';
 @import '../../material/core/style/layout-common';
-@import '../../material/core/focus-indicator/focus-indicator';
+@import '../../material/core/focus-indicators/focus-indicators';
 
 
 /// Mixin that turns on strong focus indicators.
@@ -106,8 +106,10 @@
   @if type-of($theme-or-color) != 'map' {
     @include _mat-mdc-strong-focus-indicators-border-color($theme-or-color);
   }
-  $color: mat-get-color-config($theme-or-color);
-  @if $color != null {
-    @include mat-mdc-strong-focus-indicators-color($color);
+  @else {
+    $color: mat-get-color-config($theme-or-color);
+    @if $color != null {
+      @include mat-mdc-strong-focus-indicators-color($color);
+    }
   }
 }

src/material/core/focus-indicators/_focus-indicators.scss

@@ -109,8 +109,10 @@
   @if type-of($theme-or-color) != 'map' {
     @include _mat-strong-focus-indicators-border-color($theme-or-color);
   }
-  $color: mat-get-color-config($theme-or-color);
-  @if $color != null {
-    @include mat-strong-focus-indicators-color($color);
+  @else {
+    $color: mat-get-color-config($theme-or-color);
+    @if $color != null {
+      @include mat-strong-focus-indicators-color($color);
+    }
   }
 }