Clarify when "string" should be used (and be escaped), and when
"template.HTML" should be used (no need to escape)
And help PRs like #29059 , to render the error messages correctly.
(cherry picked from commit f3eb835886031df7a562abc123c3f6011c81eca8)
Conflicts:
modules/web/middleware/binding.go
routers/web/feed/convert.go
tests/integration/branches_test.go
tests/integration/repo_branch_test.go
trivial context conflicts
65248945c9