Rewrite GitGraph.js

[zeripath]

The current vendored gitgraph.js is no longer maintained and is
difficult to understand, fix and maintain.

This PR completely rewrites its logic - hopefully in a clearer fashion
and easier to maintain.

It also includes @silverwind's improvements of coloring the commit dots
and preventing the flash of incorrect content.

Further changes to contemplate in future will be abstracting out of the
flows to an object, storing the involved commit references on the flows
etc. However, this is probably a required step for this.

Replaces #12131
Fixes #11981 (part 3)

Signed-off-by: Andrew Thornton art27@cantab.net

[zeripath]

Although this is a rewrite it may be appropriate to backport to 1.12 as the gitgraph is broken there. Otherwise we could backport a simple hacky fix that will prevent the graph from disappearing by just assigning a '#000' flow whenever a flow is missing e.g. for 1.12 apply the below patch:

diff --git a/web_src/js/vendor/gitgraph.js b/web_src/js/vendor/gitgraph.js
index 0cf5d0f75..7a5777598 100644
--- a/web_src/js/vendor/gitgraph.js
+++ b/web_src/js/vendor/gitgraph.js
@@ -376,7 +376,18 @@ export default function gitGraph(canvas, rawGraphList, config) {
           flows.splice(colomnIndex, 0, genNewFlow());
         }
 
-        color = flows[colomnIndex].color;
+        if (colomnIndex < flows.length) {
+          color = flows[colomnIndex].color;
+        } else {
+          console.error({
+            message: "Missing flow!",
+            colomnIndex,
+            colomn,
+            prevColomn,
+            flowSwapPos,
+          });
+          color = "#000";
+        }
 
         switch (colomn) {
           case '-':

[zeripath]

Good example graphs to test this can be found in #11981:

https://try.gitea.io/ahaha/glu/graph
https://try.gitea.io/ahaha/qtconnectivity/graph
https://try.gitea.io/ahaha/gitgraph/graph

[lafriks]

🚀