Put everything in Context behind the same Mutex (#1050)

* Move all interior mutability from Context to CtxRef and make it a handle
* Rename `CtxRef` to `Context`
* The old `Context` is now `ContextImpl` and is non-pub
* Add benchmark Painter::rect

Co-authored-by: Daniel Keller <dklr433@gmail.com>

epaint/src/text/font.rs

@@ -1,12 +1,11 @@
 use crate::{
-    mutex::{Mutex, RwLock},
+    mutex::{Arc, Mutex, RwLock},
     text::TextStyle,
     TextureAtlas,
 };
 use ahash::AHashMap;
 use emath::{vec2, Vec2};
 use std::collections::BTreeSet;
-use std::sync::Arc;
 
 // ----------------------------------------------------------------------------
 

epaint/src/text/fonts.rs

@@ -1,7 +1,7 @@
-use std::{collections::BTreeMap, sync::Arc};
+use std::collections::BTreeMap;
 
 use crate::{
-    mutex::Mutex,
+    mutex::{Arc, Mutex},
     text::{
         font::{Font, FontImpl},
         Galley, LayoutJob,

epaint/src/text/text_layout.rs

@@ -1,8 +1,7 @@
 use std::ops::RangeInclusive;
-use std::sync::Arc;
 
 use super::{Fonts, Galley, Glyph, LayoutJob, LayoutSection, Row, RowVisuals};
-use crate::{Color32, Mesh, Stroke, Vertex};
+use crate::{mutex::Arc, Color32, Mesh, Stroke, Vertex};
 use emath::*;
 
 /// Temporary storage before line-wrapping.

epaint/src/text/text_layout_types.rs

@@ -1,10 +1,9 @@
 #![allow(clippy::derive_hash_xor_eq)] // We need to impl Hash for f32, but we don't implement Eq, which is fine
 
 use std::ops::Range;
-use std::sync::Arc;
 
 use super::{cursor::*, font::UvRect};
-use crate::{Color32, Mesh, Stroke, TextStyle};
+use crate::{mutex::Arc, Color32, Mesh, Stroke, TextStyle};
 use emath::*;
 
 /// Describes the task of laying out text.