This commit changes the default file extension for Freemarker templates
from `*.ftl` to `*.ftlh`. This commit also enables by default the
Freemarker setting `"recognize_standard_file_extensions"` to ensure that
HTML escaping is performed by default in Spring Boot applications.
Applications should adapt to this change by changing the file extensions
of existing templates to `.ftlh`.
Closes gh-15131
7a9d1a1e34