Git: Add instant line annotation (blame)

Inspired by the Visual Studio Code plugin GitLens.

Add an annotation to the editor line the cursor
is  currently in. A tooltip contains the commit
data and allows to invoke git show for the commit.

When the automatic annotation is turned off, it can
still be forced for the current line with an action.
The default shortcut for this action is: Alt+G,Alt+I

Task-number: QTCREATORBUG-23299
Change-Id: I58eef9efcf531afb11470e5f5456e19f282b18d0
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/git/gitsettings.cpp

@@ -88,6 +88,13 @@ GitSettings::GitSettings()
     repositoryBrowserCmd.setDisplayName(Tr::tr("Git Repository Browser Command"));
     repositoryBrowserCmd.setLabelText(Tr::tr("Command:"));
 
+    registerAspect(&instantBlame);
+    instantBlame.setSettingsKey("Git Instant");
+    instantBlame.setDefaultValue(true);
+    instantBlame.setLabelText(Tr::tr("Add instant blame annotations to editor"));
+    instantBlame.setToolTip(Tr::tr("Directly annotate each line in the editor "
+                                   "when scrolling through the document."));
+
     registerAspect(&graphLog);
     graphLog.setSettingsKey("GraphLog");
 
@@ -173,6 +180,11 @@ GitSettingsPage::GitSettingsPage(GitSettings *settings)
                 Row { s.repositoryBrowserCmd }
             },
 
+            Group {
+                title(Tr::tr("Instant Blame")),
+                Row { s.instantBlame }
+            },
+
             st
         }.attachTo(widget);
     });