bug#40268: 27.0.60; [PATCH] Unify and improve gdb-mi source window display

[Yuan Fu]

Before this change, stepping and other gdb command handlers use 
'gud-display-line’ and 'gdb-goto-breakpoint' uses 'gdb-display-source-buffer'.  
Now whenever gdb-mi code tries to open a source buffer, 
'gdb-display-source-buffer’ is used.  Also, we simplify the logic in 
'gdb-display-source-buffer’ and add a feature to limit the maximum number of 
source windows.

From a user’s perspective, this change solves two problems: 1. The behavior 
difference between jumping to break point and stepping (and other command) 2. 
Gdb-mi opening more windows than I wanted for displaying source files.

Yuan

source-window.patch
Description: Binary data

In GNU Emacs 27.0.60 (build 1, x86_64-apple-darwin19.3.0, NS appkit-1894.30 
Version 10.15.3 (Build 19D76))
of 2020-02-25 built on missSilver
Repository revision: f27187f963e9e36435b508e29256e048799e0ff2
Repository branch: emacs-27
Windowing system distributor 'Apple', version 10.3.1894
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