refactor: update image source documentation snippets and tests (#5390)

tests/app/image-source/image-source.md

@@ -7,24 +7,50 @@ previous_url: /ApiReference/image-source/HOW-TO
 ---
 # Image source
 Using the image source requires the image-source module.
-{%snippet imagesource-require%}
+```TypeScript
+import * as imageSource from "tns-core-modules/image-source";
+```
+```JavaScript
+var imageSource = require("tns-core-modules/image-source");
+```
 The pre-required `imageSource` module is used throughout the following code snippets.
 We also use fs module defined as follows:
-{%snippet imagesource-require-alt%}
+```TypeScript
+import * as fs from "tns-core-modules/file-system";
+```
+```JavaScript
+var fs = require("tns-core-modules/file-system");
+```
 
 ## Loading and saving images
+
 ### Load image using resource name
-This is similar to loading Bitmap from `R.drawable.logo` on Android or calling `[UIImage imageNamed@"logo"]` on iOS
+This is similar to loading Bitmap from `R.drawable.logo` on Android or calling `[UIImage imageNamed@"logo"]` on iOS.
+The method `fromResource` creates an `ImageSource` instance and loads it from the specified resource name.
 {%snippet imagesource-resname%}
 
-### Load image from URL
-{%snippet imagesource-load-url%}
-
-### Save image source to PNG or JPG file
+### Save image to PNG or JPG file
+The method `saveToFile(path: string, format: "png" | "jpeg" | "jpg", quality?: number): boolean` saves `ImageSource` instance to the specified file, using the provided image format and quality.
+The supported formats are `png`, `jpeg`, and `jpg`. The quality parameter is optional and defaults to maximum quality. Returns `true` if the file is saved successfully.
 {%snippet imagesource-save-to%}
 
 ### Load image from a local file
+Use `fromFile(path: string): Promise<boolean>` to load an `ImageSource` instance from the specified file asynchronously.
 {%snippet imagesource-load-local%}
 
-### Save image source from imageAsset to PNG file
-{%snippet imagesource-from-imageasset-save-to%}
+### Load image from URL
+Use `http.getImage(url: string): Promise<ImageSource>` to fetch `ImageSource` from online source.
+{%snippet http-get-image%}
+
+### Save image from image asset to PNG file
+Use `fromAsset(asset: ImageAsset): Promise<ImageSource>` to load `ImageSource` from the specified `ImageAsset` asynchronously.
+{%snippet imagesource-from-imageasset-save-to%}
+
+### Creating base64 string from PNG image file
+The method `toBase64String(format: "png" | "jpeg" | "jpg", quality?: number): string` converts the image to base64 encoded string, using the provided image format and quality.
+The supported formats are `png`, `jpeg`, and `jpg`. The quality parameter is optional and defaults to maximum quality.
+{%snippet imagesource-to-base-string%}
+
+### Creating PNG image file from base64 string
+The method `fromBase64(source: string): Promise<boolean>` loads this instance from the specified base64 encoded string asynchronously.
+{%snippet imagesource-from-base-string%}