Only cache template digests if config.cache_template_loading

since ActionView::Resolver.caching is set to the same value as config.cache_template_loading
only cache template digests if config.cache_template_loading is not falsy
fixes issues #10752 and #10791
Updating README.md [ci skip]

Updating the global Rails README following work by @strzalek et al which extracted Action View to a separate gem, and also some other improvements.

Summary of changes:

* Reordered the paragraphs from View-Model-Controller to Model-Controller-View, based on how (IMHO) most people think about the structure and hierarchy of the framework and their code in it.
* Added references to ActionView's README in the _View_ paragraph
* Reworded the _Controller_ paragraph to briefly mentioned routing as handled by Action Dispatch, and that both Action Dispatch and Action Controller work together to form the request-handling Action Pack
* Removed paragraph saying Action Pack is coupled with Action View, as this is no longer the case
* Added brief references to Action Mailer and Active Support, since they are both major Rails components. Briefly mentioned in the _View_ paragraph that Action View is often used to generate the body of the email, in addition to the other typical of using to build a response body.
Perf: fields in pg gem causes an allocation, cache it
Perf: avoid array allocation where not needed
Merge pull request #12037 from SamSaffron/mem_alloc

Performance: Reduce memory allocations in Active Record
Merge pull request #12038 from SamSaffron/memoize_decorate_cols

Perf: memoize serialized column list and time zone column list
Improve AP changelog regarding AV extraction [ci skip]
Ensure all-caps nested consts marked as autoloaded

Previously, an autoloaded constant `HTML::SomeClass` would not be marked
as autoloaded by AS::Dependencies. This is because the
`#loadable_constants_for_path` method uses `String#camelize` on the
inferred file path, which in turn means that, unless otherwise directed,
AS::Dependencies watches for loaded constants in the `Html` namespace.

By passing the original qualified constant name to `#load_or_require`,
this inference step is avoided, and the new constant is picked up in the
correct namespace.
Merge pull request #11636 from urbanautomaton/uppercase-nested-const-autoload-marking

`ActiveSupport::Dependencies`: consts in uppercase nestings not marked as autoloaded
check class hierarchy with is_a? in PredicateBuilder.expand

add changelog entry for #11945
adding more finder migration information to upgrade guide [ci skip]
Merge pull request #12030 from garysweaver/master

adding more finder deprecation info in upgrade documentation [ci skip]
Merge pull request #12028 from egilburg/patch-1

Updating Rails README.md to reflect current state [ci skip]
Fix misspelling on README.md

[ci skip]
Merge pull request #11945 from Mik-die/polymorphic-decorator

check class hierarchy with is_a? in PredicateBuilder.expand
 #11803: Move Forbidden attributes description before show post section

[ci skip]
Remove gist link from the code

It is not good to include links in the code. These links can be in the
future outdated and nobody will upgrade they.

[ci skip]
Merge pull request #11805 from jetthoughts/11803_update_move_forbidden_exception_description_before_show

[Getting Started Guide] Move Forbidden attributes description before show post section [ci skip]
Merge pull request #11768 from cloudspace/cache_template_loading

Only cache template digests if !config.cache_template_loading
Improve CHANGELOG entry [ci skip]