Add Tabular Diff for CSV files (#14661)

Implements request #14320 The rendering of CSV files does match the diff style.

* Moved CSV logic into base package.

* Added method to create a tabular diff.

* Added CSV compare context.

* Added CSV diff template.

* Use new table style in CSV markup.

* Added file size limit for CSV rendering.

* Display CSV parser errors in diff.

* Lazy read single file.

* Lazy read rows for full diff.

* Added unit tests for various CSV changes.

modules/setting/setting.go

@@ -213,6 +213,10 @@ var (
 			Enabled bool `ini:"ENABLE_RENDER"`
 		} `ini:"ui.svg"`
 
+		CSV struct {
+			MaxFileSize int64
+		} `ini:"ui.csv"`
+
 		Admin struct {
 			UserPagingNum   int
 			RepoPagingNum   int
@@ -258,6 +262,11 @@ var (
 		}{
 			Enabled: true,
 		},
+		CSV: struct {
+			MaxFileSize int64
+		}{
+			MaxFileSize: 524288,
+		},
 		Admin: struct {
 			UserPagingNum   int
 			RepoPagingNum   int