[5.x] More Antlers defaults

[jasonvarga]

This builds on #14092 and does the following:

• Tags and modifiers within the App namespace (i.e. your own tags/modifiers) are automatically allowed. Any knowledge of your own code would be internal and presumably safe.
• Adds a bunch more safe core modifiers to the defaults.

[daun]

@jasonvarga This only applies to Antlers in content fields, right? Meaning templates/views would still allow any modifiers including those from the vendor folder? Just making sure since we tend to package our common modifiers and use them from a composer package.

[jasonvarga]

Yes. In actual templates you can continue to do whatever you want.

[efc]

Where can we find a list of the "safe core" modifiers and tags?