Filling out line level coverage for base, base-core, widget

Added new _NON_ATTRS_CFG static to Base._buildCfg, for custom aggregation

Trailing comma cleanup

Cleaned up Ext._buildCfg support. All buildCfg meta-data now merged into a single shared hash, used for all static/aggregate/custom mixing. Added Ext._buildCfg test cases for static/aggregate/custom support. Also removed statics:true support. See #2531567

Ext._buildCfg support - initial drop

Avoid repeating Base constructor logic (and kicking off another init chain) when constructor is called more than once (e.g. when using Base.create with an extension which also inherits from Base)

Prepped tests for coverage reporting

Base.create/mix will now treat initializer and destructor methods on Extension prototypes in the same way it does for the host class. Extension initializer prototype methods will be invoked after the initializer of the host class. Extension destructor methods will be invoked before the host class destructor. Extensions which were previously using the init event, or the initializedChange event, or AOP in their constructors to inject logic after the host class initializer, can just define an initializer function instead. Fixes #2528546