Add Page.Contents with scope support

Note that this also adds a new `.ContentWithoutSummary` method, and to do that we had to unify the different summary types:

Both `auto` and `manual` now returns HTML. Before this commit, `auto` would return plain text. This could be considered to be a slightly breaking change, but for the better: Now you can treat the `.Summary` the same without thinking about where it comes from, and if you want plain text, pipe it into `{{ .Summary | plainify }}`.

Fixes #8680
Fixes #12761
Fixes #12778
Fixes #716

common/paths/pathparser.go

@@ -153,7 +153,7 @@ func (pp *PathParser) doParse(component, s string, p *Path) (*Path, error) {
 				} else {
 					high = len(p.s)
 				}
-				id := types.LowHigh{Low: i + 1, High: high}
+				id := types.LowHigh[string]{Low: i + 1, High: high}
 				if len(p.identifiers) == 0 {
 					p.identifiers = append(p.identifiers, id)
 				} else if len(p.identifiers) == 1 {
@@ -260,7 +260,7 @@ type Path struct {
 	component  string
 	bundleType PathType
 
-	identifiers []types.LowHigh
+	identifiers []types.LowHigh[string]
 
 	posIdentifierLanguage int
 	disabled              bool