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
add empty_data option where required option is used
add missing code-block directive
add note when forbidding access to anonymous users on custom authentication provider
answer some questions and clarify the best chapter imo from the symfony documentation
address comments from @WouterJ
[#3424] Backporting a change to 2.3
[Reference][Form Types] Document "with_minutes" time/datetime option
Fix "versionadded" position
add max_length to form field type
fix typo in previous commit
fix typo in previous commit
fix last typo on max length option
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