Include build number in Positron version string for better version tracking (i.e. for dailies) (#11008)

Addresses #10688

In this PR, I updated the version string to include both the version and
build number so that folks on daily builds can also get those bootstrap
installed extensions working correctly.

I think the best way to check that this is working correctly is to
simulate a build number change by manually editing
`~/.positron-dev/extensions/.version` to have a different build number.

@:extensions

### Release Notes

#### New Features

- N/A

#### Bug Fixes

- Fixed how bootstrap installed extensions check Positron's version so
that the dailies get correct extensions installed.


### QA Notes

You can also simulate a build number change by manually editing the
`.version` file for your _release_ build, i.e. at
`~/.positron/extensions/.version`, or alternatively, you could carefully
notice when you get a daily build update and see that the bootstrap
extensions get installed afresh.

You can see when this happens in the "Shared" output channel, with a
message like:

> [info] [Shared] First launch after first install, upgrade, or
downgrade. Installing bootstrapped extensions

Author: juliasilge

src/vs/platform/extensionManagement/node/positronBootstrapExtensionsInitializer.ts

@@ -27,7 +27,7 @@ export class PositronBootstrapExtensionsInitializer extends Disposable {
 		super();
 
 		const storageFilePath = join(this.environmentService.extensionsPath, '.version');
-		const currentVersion = this.productService.positronVersion;
+		const currentVersion = `${this.productService.positronVersion}-${this.productService.positronBuildNumber}`;
 
 		const lastKnownVersion = existsSync(storageFilePath) ? readFileSync(storageFilePath, 'utf8').trim() : '';