Text in the theme's primary text colour unless given another, rather than white

A `Text` given no colour was drawn white, which on a light theme's white surfaces could not be read: Prompt's dialog to share tabs showed neither the code nor the time left in it, and the titles of the clip_path, file_chooser and tab_strip examples, drawn over the theme's background, did not show in the light theme. `Text::new` now takes the theme's `text_primary`, as the toast, the text field and the pickers already do, so a label given no colour reads on light and dark themes alike. Its documentation and the test of its defaults say so.

src/widget/text/mod.rs

@@ -66,15 +66,15 @@ pub struct Text
 
 impl Text
 {
-	/// A left-aligned, non-wrapping, ellipsis-truncated white label at the
-	/// default 16 px size with the canvas default font.
+	/// A left-aligned, non-wrapping, ellipsis-truncated label in the theme's
+	/// primary text colour at the default 16 px size with the canvas default font.
 	pub fn new( content: impl Into<String> ) -> Self
 	{
 		Self
 		{
 			content:  content.into(),
 			size:     Length::px( 16.0 ),
-			color:    Color::WHITE,
+			color:    crate::theme::palette().text_primary,
 			align:    TextAlign::Left,
 			wrap:     false,
 			truncate: true,

src/widget/text/tests.rs

@@ -12,7 +12,7 @@ fn new_uses_documented_defaults()
 	let t = Text::new( "hello" );
 	assert_eq!( t.content, "hello" );
 	assert_eq!( t.size,    crate::Length::px( 16.0 ) );
-	assert_eq!( t.color,   Color::WHITE );
+	assert_eq!( t.color,   crate::theme::palette().text_primary );
 	assert_eq!( t.align,   TextAlign::Left );
 }