docs: add how context strategies work

docs/en/UI/Angular/Context-Strategy.md

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+# ContextStrategy
+
+`ContextStrategy` is an abstract class exposed by @abp/ng.core package. There are three context strategies extending it: `ComponentContextStrategy`, `TemplateContextStrategy`, and `NoContextStrategy`. Implementing the same methods and properties, all of these strategies help you define how projected content will get their context.
+
+
+
+## ComponentContextStrategy
+
+`ComponentContextStrategy` is a class that extends `ContextStrategy`. It lets you **pass context to a projected component**.
+
+
+### constructor
+
+```js
+constructor(public context: Partial<InferredInstanceOf<T>>) {}
+```
+
+- `T` refers to component type here, i.e. `Type<C>`.
+- `InferredInstanceOf` is a utility type exposed by @abp/ng.core package. It infers component shape.
+- `context` will be mapped to properties of the projected component.
+
+
+### setContext
+
+```js
+setContext(componentRef: ComponentRef<InferredInstanceOf<T>>): Partial<InferredInstanceOf<T>>
+```
+
+This method maps each prop of the context to the component property with the same name and calls change detection. It returns the context after mapping.
+
+
+
+## TemplateContextStrategy
+
+`TemplateContextStrategy` is a class that extends `ContextStrategy`. It lets you **pass context to a projected template**.
+
+
+### constructor
+
+```js
+constructor(public context: Partial<InferredContextOf<T>>) {}
+```
+
+- `T` refers to template context type here, i.e. `TemplateRef<C>`.
+- `InferredContextOf` is a utility type exposed by @abp/ng.core package. It infers context shape.
+- `context` will be mapped to properties of the projected template.
+
+
+### setContext
+
+```js
+setContext(): Partial<InferredContextOf<T>>
+```
+
+This method does nothing and only returns the context, because template context is not mapped but passed in as parameter to `createEmbeddedView` method.
+
+
+
+## NoContextStrategy
+
+`NoContextStrategy` is a class that extends `ContextStrategy`. It lets you **skip passing any context to projected content**.
+
+
+### constructor
+
+```js
+constructor()
+```
+
+Unlike other context strategies, `NoContextStrategy` contructor takes no parameters.
+
+
+### setContext
+
+```js
+setContext(): undefined
+```
+
+Since there is no context, this method gets no parameters and will return `undefined`.
+
+
+
+## Predefined Context Strategies
+
+Predefined context strategies are accessible via `CONTEXT_STRATEGY` constant.
+
+
+### None
+
+```js
+CONTEXT_STRATEGY.None()
+```
+
+This strategy will not pass any context to the projected content.
+
+
+### Component
+
+```js
+CONTEXT_STRATEGY.Component(context: Partial<InferredContextOf<T>>)
+```
+
+This strategy will help you pass the given context to the projected component.
+
+
+### Template
+
+```js
+CONTEXT_STRATEGY.Template(context: Partial<InferredContextOf<T>>)
+```
+
+This strategy will help you pass the given context to the projected template.
+
+
+## See Also
+
+- [ProjectionStrategy](./Projection-Strategy.md)