feat: add tracker context

src/tracker-context/index.ts

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+export { createTrackerContext } from './tracker-context'
+export type { TrackerContext } from './tracker-context-types'

src/tracker-context/tracker-context-types.ts

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+import type { EventProperties } from '../data-layer'
+
+/**
+ * Tracker context scope.
+ * @public
+ */
+export type TrackerContext = Readonly<{
+  /**
+   * An object containing the context properties.
+   * @internal
+   */
+  context: { readonly value: EventProperties }
+
+  /**
+   * Sets context properties.
+   *
+   * It could be used to set or update properties in this context.
+   * @public
+   * @example
+   * const context = createTrackerContext({ userId: 'not defined' })
+   * context.setProps({ userId: '2f9kfo7', foo: 'bar' })
+   */
+  setProps: (props: EventProperties) => void
+}>

src/tracker-context/tracker-context.ts

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+import type { EventProperties } from '../data-layer'
+import type { TrackerContext } from './tracker-context-types'
+
+/**
+ * Creates a context for track events.
+ *
+ * All properties in this context will be injected into every
+ * track event that uses this context.
+ *
+ * @param initialProps - Properties witch will initialize the context.
+ * @public
+ * @example
+ * createTrackerContext({
+ *   appVersion: '1.2.7',
+ *   userId: getUserIdFromSomewhere()
+ *   // Properties you need to send in all track events
+ * })
+ */
+export function createTrackerContext(
+  initialProps: EventProperties = {}
+): TrackerContext {
+  const context = { value: { ...initialProps } }
+
+  function setProps(props: EventProperties) {
+    context.value = { ...props }
+  }
+
+  return { context, setProps }
+}