Transparent video read/write support (#145)

* Add support for reading transparent Matroska and implement alpha side data & decode

* Few fixes

* Implement alpha encoding

* Gracefully handle inability to acquire WebGL context, properly clean up WebGL contexts

* Improve touch device detection

* Test test

* Test test #2

* Test test 3

* Test test 4

* Test test 5

* Test test 6

* Test test 7

* Test test 8

* Test test 9

* Test test 10

* Test test 11

* Test test 12

* Test test 13

* Test test 14

* Test test 15

* Test test 16

* Test test 17

* Test test 18

* Test test 19

* Test test 20

* Fix type errors, improve MetadataTags docs

* Do a bunch of docs work

* Test test?

* "Unexpected only modifier 🤓"

* Add InputVideoTrack.canBeTransparent()

* Some clean-up

* Adjust CI to be less spammy in PRs

* Fix broken license headers

src/sample.ts

@@ -96,6 +96,14 @@ export class VideoSample {
 		return Math.trunc(SECOND_TO_MICROSECOND_FACTOR * this.duration);
 	}
 
+	/**
+	 * Whether this sample uses a pixel format that can hold transparency data. Note that this doesn't necessarily mean
+	 * that the sample is transparent.
+	 */
+	get hasAlpha() {
+		return this.format && this.format.includes('A');
+	}
+
 	/**
 	 * Creates a new {@link VideoSample} from a
 	 * [`VideoFrame`](https://developer.mozilla.org/en-US/docs/Web/API/VideoFrame). This is essentially a near zero-cost