docs($provide): fix Markdown formatting for provider method

Indentation made Markdown parser think that it’s a block of code.

Closes #5446
docs($http): remove outdated part about $http outside of $apply phase

This removes some outdated advice which no longer is true against the latest angular version.

The information about unit testing with ngMocks remains, because it's always good to have
information like that easily found. This little snippet is not worded perfectly, and is not
a very good example unit test, so additional work is needed here.

Relates to #5206
Closes #5485
docs(ngEventDirs): document priority of event directives

The general assumption is that if @priority is not defined, the priority is 0. BUT it's not
necessarily harmful to be explicit about this.

Closes #5852