Update forms.rst

Accessing form values via `vars` property instead of getter. Updated PHP templating examples.
Update forms.rst

Accessing form values via `vars` property instead of getter. Updated PHP templating examples.
merge
Fixed vars as object property, not array
syntax error corrected
add default value to mapped option of entity
document auto_initialize overriden option
[#3407] Re-wording things so that people don't pay too much attention to auto_initialize
Use static Request methods in Trusting Proxies doc

As these methods manipulate static properties, it makes sense to use the static methods. This also means that we don't need to create a throwaway Request instance just to set the trusted proxies.
Merge pull request #3409 from kuusas/patch-1

Update forms.rst
Merge branch '2.3' into 2.4