Unicode art for symbolics

[vbraun]

Example:

sage: %display unicode_art
sage: integral(exp(sqrt(x))/(x+pi), x)
⌠          
⎮    ___   
⎮  ╲╱ x    
⎮ ℯ        
⎮ ────── dx
⎮ x + π    
⌡          

Depends on #18357

CC: @videlec

Component: symbolics

Author: Volker Braun

Branch/Commit: db1c0e4

Reviewer: Vincent Delecroix

Issue created by migration from https://trac.sagemath.org/ticket/18482

[vbraun]

Dependencies: #18357

[vbraun]

Description changed:

--- 
+++ 
@@ -1 +1,13 @@
+Example:
 
+```
+sage: %display unicode_art
+sage: integral(exp(sqrt(x))/(x+pi), x)
+⌠          
+⎮    ___   
+⎮  ╲╱ x    
+⎮ ℯ        
+⎮ ────── dx
+⎮ x + π    
+⌡          
+```

[vbraun]

Author: Volker Braun

[vbraun]

Branch: u/vbraun/unicode_art_for_symbolics

[sagetrac-git]

Commit: ef5b6a4

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

ef5b6a4

fix docbuild and doctests in sage.typeset

[videlec]

Work Issues: rebase

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

3f68c33

Merge 6.8.beta2 into #18482