[IMP] web, *: stop automatic color for text for transparent bg classes

* web_editor

Now, if the opacity of the bg color for a bg classes is lower than x
(currently 0.3), the class will only control the bg and not the text
and other components anymore. This behavior is disabled for presets
though (otherwise the text color would be "undefined").

Part of https://github.com/odoo/odoo/pull/45856
task-2197038

addons/web/static/src/scss/bs_mixins_overrides.scss

@@ -27,15 +27,18 @@ $enable-deprecation-messages: false !default;
     }
 }
 
+$o-yiq-min-opacity-threshold: 0.3 !default;
 $o-color-extras-nesting-selector: '&' !default;
 
-@mixin o-bg-color($color, $text-color: null, $with-extras: true, $important: true, $nesting-selector: $o-color-extras-nesting-selector) {
+@mixin o-bg-color($color, $text-color: null, $with-extras: true, $important: true, $yiq-min-opacity-threshold: $o-yiq-min-opacity-threshold, $nesting-selector: $o-color-extras-nesting-selector) {
     @if ($color) {
-        $-yiq-color: if($text-color, $text-color, color-yiq($color));
+        $-yiq-threshold-met: alpha($color) > $yiq-min-opacity-threshold;
+
+        $-yiq-color: if($text-color, $text-color, if($-yiq-threshold-met, color-yiq($color), null));
         background-color: $color#{if($important, ' !important', '')};
         color: $-yiq-color; // not important so that text utilities still work
 
-        @if $with-extras {
+        @if $with-extras and $-yiq-threshold-met {
             #{$nesting-selector} {
                 @extend %o-bg-color-component-color-reset;
 

addons/web_editor/static/src/scss/web_editor.common.scss

@@ -615,7 +615,7 @@ blockquote {
     // bg and text utility classes. **
     .o_cc#{$index} {
         // Background & Text
-        @include o-bg-color(o-color($-bg), o-color($-text), $important: false);
+        @include o-bg-color(o-color($-bg), o-color($-text), $important: false, $yiq-min-opacity-threshold: 0);
 
         #{$o-color-extras-nesting-selector} {
             // Headings