[Proposal] add getters for Blade's contentTags and escapedContentTags

Some people that are using Javascript front end frameworks are changing the Blade content tags using the `Blade:setContentTags('[[', ']]')` and `Blade:setEscapedContentTags('[[[', ']]]')` which sets a different set of tags for defining Blade syntax in a view.

Currently there are only setters for the `contentTags` protected properties of the `BladeCompiler` class. Therefore, it is not easily possible to retrieve these values with something like `Blade:getContentTags()` and `Blade:setEscapedContentTags()`.