Add import documentation snippet to component doc pages (#7535)

Author: ggdouglas

packages/core/src/components/alert/alert.md

@@ -2,6 +2,12 @@
 
 **Alerts** notify users of important information and force them to acknowledge the alert content before continuing.
 
+@## Import
+
+```tsx
+import { Alert } from "@blueprintjs/core";
+```
+
 Although similar to [**Dialog**](#core/components/dialog), an alert is more restrictive and should only be used for
 important information. By default, the user can only exit the alert by clicking one of the confirmation buttons;
 clicking the overlay or pressing the `esc` key will not close the alert. These interactions can be enabled via props.

packages/core/src/components/context-menu/context-menu.md

@@ -4,6 +4,12 @@
 They essentially generate an opinionated [**Popover**](#core/components/popover) instance configured
 with the appropriate interaction handlers.
 
+@## Import
+
+```tsx
+import { ContextMenu } from "@blueprintjs/core";
+```
+
 @reactExample ContextMenuExample
 
 @## Usage

packages/core/src/components/dialog/dialog.md

@@ -3,6 +3,12 @@
 The **Dialog** component presents content overlaid over other parts of the UI via
 [**Overlay2**](#core/components/overlay2).
 
+@## Import
+
+```tsx
+import { Dialog } from "@blueprintjs/core";
+```
+
 <div class="@ns-callout @ns-intent-primary @ns-icon-info-sign @ns-callout-has-body-content">
     <h5 class="@ns-heading">Terminology note</h5>
 

packages/core/src/components/drawer/drawer.md

@@ -3,6 +3,12 @@
 **Drawers** overlay content over existing parts of the UI and are anchored to the edge of the screen.
 It is built using the lower-level [**Overlay2**](#core/components/overlay2) component.
 
+@## Import
+
+```tsx
+import { Drawer } from "@blueprintjs/core";
+```
+
 @reactExample DrawerExample
 
 @## Usage

packages/core/src/components/entity-title/entity-title.md

@@ -2,6 +2,12 @@
 
 **EntityTitle** is a component that handles rendering a common UI pattern consisting of title, icon, subtitle and tag.
 
+@## Import
+
+```tsx
+import { EntityTitle } from "@blueprintjs/core";
+```
+
 @reactExample EntityTitleExample
 
 @## Props interface

packages/core/src/components/forms/checkbox.md

@@ -2,6 +2,12 @@
 
 A checkbox allows the user to toggle between checked, unchecked, and (sometimes) indeterminate states.
 
+@## Import
+
+```tsx
+import { Checkbox } from "@blueprintjs/core";
+```
+
 @reactExample CheckboxExample
 
 @## Usage

packages/core/src/components/forms/control-group.md

@@ -16,6 +16,12 @@ promoted to live in a control group.
 
 </div>
 
+@## Import
+
+```tsx
+import { ControlGroup } from "@blueprintjs/core";
+```
+
 @reactExample ControlGroupExample
 
 @## Flex layout

packages/core/src/components/forms/file-input.md

@@ -2,6 +2,12 @@
 
 **FileInput** is a lightweight wrapper around a `<label>` container element which contains an `<input type="file">`.
 
+@## Import
+
+```tsx
+import { FileInput } from "@blueprintjs/core";
+```
+
 @reactExample FileInputExample
 
 @## Usage

packages/core/src/components/forms/form-group.md

@@ -4,6 +4,12 @@ Form groups support more complex form controls than [simple labels](#core/compon
 such as [control groups](#core/components/control-group) or [`NumericInput`](#core/components/numeric-input).
 They also support additional helper text to aid with user navigation.
 
+@## Import
+
+```tsx
+import { FormGroup } from "@blueprintjs/core";
+```
+
 @reactExample FormGroupExample
 
 @## Props

packages/core/src/components/forms/input-group.md

@@ -4,6 +4,12 @@
 This component allows you to optionally add icons and buttons _within_ a text input to expand its appearance and
 functionality. For example, you might use an input group to build a visibility toggle for a password field.
 
+@## Import
+
+```tsx
+import { InputGroup } from "@blueprintjs/core";
+```
+
 @reactExample InputGroupExample
 
 @## Usage