Allow quoting hypertext attribute values

[rubenwardy]

Hypertext markup attributes cannot contain spaces currently. This is a huge limitation, especially when showing images in the main menu - if the path to the image contains a space then it cannot be shown in current master.

This PR allows quoting hypertext attribute values, like in HTML.

To do

This PR is Ready for Review.

Should we deprecate unquoted attribute values? Or should we immediately remove support for unquoted attributes as hypertext is experimental? HTML supports unquoted attribute values

How to test

• Checkout the ContentDB redesign. Build/install minetest on a path with space.
• Open NodeCore in the CDB dialog, see broken img tags
• Apply this PR and the following patch. The img tags should now work

diff --git a/builtin/mainmenu/content/dlg_package.lua b/builtin/mainmenu/content/dlg_package.lua
index ed1ab97ff..63b59a0cf 100644
--- a/builtin/mainmenu/content/dlg_package.lua
+++ b/builtin/mainmenu/content/dlg_package.lua
@@ -165,11 +165,11 @@ local function get_formspec(data)
                        local fs_to_px = winfo.size.x / winfo.max_formspec_size.x
                        for i, ss in ipairs(info.screenshots) do
                                local path = get_screenshot(data.package, ss.url, 2)
-                               hypertext = hypertext .. "<action name=ss_" .. i .. "><img name=" ..
-                                               core.hypertext_escape(path) .. " width=" .. (3 * fs_to_px) ..
+                               hypertext = hypertext .. "<action name=ss_" .. i .. "><img name=\"" ..
+                                               core.hypertext_escape(path) .. "\" width=" .. (3 * fs_to_px) ..
                                                " height=" .. (2 * fs_to_px) .. "></action>"
                                if i ~= #info.screenshots then
-                                       hypertext = hypertext .. "<img name=blank.png width=" .. (0.25 * fs_to_px) ..
+                                       hypertext = hypertext .. "<img name=\"blank.png\" width=" .. (0.25 * fs_to_px) ..
                                                        " height=" .. (2.25 * fs_to_px).. ">"
                                end
                        end
@@ -177,7 +177,7 @@ local function get_formspec(data)
                                        info.long_description.body
 
                        hypertext = hypertext:gsub("<img name=blank.png ",
-                                       "<img name=" .. core.hypertext_escape(defaulttexturedir) .. "blank.png ")
+                                       "<img name=\"" .. core.hypertext_escape(defaulttexturedir) .. "blank.png\" ")
 
                        table.insert_all(formspec, {
                                "hypertext[0.375,0;",

[rubenwardy]

Updated to support single quotes (')

[rubenwardy]

You can no longer use the escape character to escape in unquoted attribute values

[sfan5]

LGTM, not tested