Include base/ platform from VS Code, adopt DomScrollableElement and introduce esbuild

[Tyriar]

Succeeds https://github.com/xtermjs/xterm.js/pull/5076

[Tyriar]

I stopped this briefly to work on some debt and to bring some of the changes here into main in smaller PRs. Doing some tables to better understand where we want to go:

Here is the current main output usage:

Use	Path	Format	Runtime	Note
Demo (/ and /test)	demo/dist/client-bundle.js	bundle	browser	Used in API/playwright tests
	out/	tsc	-	Used for core and addons
Unit tests	out/	tsc	node.js	Running in a real browser would be nice
API tests	out-test/api/	tsc	node.js	Removed in #5080
Integration tests	out-test/playwright/	tsc	node.js
Benchmark	out-test/benchmark/	tsc	node.js
@xterm/xterm package	lib/xterm.js	bundle	browser
@xterm/headless package	headless/lib-headless/xterm-headless.js	bundle	node.js

And the current output usage on this branch (I think):

Use	Path	Format	Runtime	Note
Demo (/ and /test)	demo/dist/client-bundle.js	bundle	browser	Used in API/playwright tests
	out-tsc/	tsc	-	Used for image addon only
	out-esbuild/	esbuild	-	Used for ligatures addon only
	lib/	esbuild	-	Used for core and other addons (this might require packaging atm?)
Unit tests	out-tsc/	tsc	node.js	Running in a real browser would be nice
API tests	out-tsc/test-api/	tsc	node.js
Integration tests	out-tsc/test-playwright/	tsc	node.js
Benchmark	out-tsc/test-benchmark/	tsc	node.js
@xterm/xterm package	lib/xterm.js	bundle	browser
@xterm/headless package	headless/lib-headless/xterm-headless.js	bundle	node.js

[Tyriar]

main:

Proposal (probably needs a different PR):