Escape HTML in theme author name to allow for ampersands

[morganestes]

In wp-admin/themes.php, the template prints & to the screen if there's an ampersand in the author name (multiple theme authors using "&" instead of "and".

Tested in trunk after THX38, not sure if it was in there before. #24775 references a similar issue.

Changing from {{ data.author }} to {{{ data.author }}} fixes the issue when displaying the theme details overlay.

[morganestes]

If #26098 is applied, this is the combined patch.

[morganestes]

Two new diffs added since data.author is actually located in two places.

26100.diff is the fix just for this ticket.
26100.1.diff is the fix if #26098 is already applied, since it has some overlap that causes changes that affect where this code is.

[dd32]

In 26316:

Themes: Move the escaping of content from JS back to PHP. This allows us to take advantage of the display() WP_Theme method to translate the text properly, and to strip out any HTML tags we don't wish to display. Fixes #26100. See #25948