Refactor some Str2html code (#29397)

This PR touches the most interesting part of the "template refactoring".

1. Unclear variable type. Especially for "web/feed/convert.go":
sometimes it uses text, sometimes it uses HTML.
2. Assign text content to "RenderedContent" field, for example: `
project.RenderedContent = project.Description` in web/org/projects.go
3. Assign rendered content to text field, for example: `r.Note =
rendered content` in web/repo/release.go
4. (possible) Incorrectly calling `{{Str2html
.PackageDescriptor.Metadata.ReleaseNotes}}` in
package/content/nuget.tmpl, I guess the name Str2html misleads
developers to use it to "render string to html", but it only sanitizes.
if ReleaseNotes really contains HTML, then this is not a problem.

routers/web/org/projects.go

@@ -19,6 +19,7 @@ import (
 	"code.gitea.io/gitea/modules/base"
 	"code.gitea.io/gitea/modules/json"
 	"code.gitea.io/gitea/modules/setting"
+	"code.gitea.io/gitea/modules/templates"
 	"code.gitea.io/gitea/modules/util"
 	"code.gitea.io/gitea/modules/web"
 	shared_user "code.gitea.io/gitea/routers/web/shared/user"
@@ -104,7 +105,7 @@ func Projects(ctx *context.Context) {
 	}
 
 	for _, project := range projects {
-		project.RenderedContent = project.Description
+		project.RenderedContent = templates.Str2html(project.Description) // FIXME: is it right? why not render?
 	}
 
 	err = shared_user.LoadHeaderCount(ctx)
@@ -395,7 +396,7 @@ func ViewProject(ctx *context.Context) {
 		}
 	}
 
-	project.RenderedContent = project.Description
+	project.RenderedContent = templates.Str2html(project.Description) // FIXME: is it right? why not render?
 	ctx.Data["LinkedPRs"] = linkedPrsMap
 	ctx.Data["PageIsViewProjects"] = true
 	ctx.Data["CanWriteProjects"] = canWriteProjects(ctx)