build: make sdl scan gulp tasks lazy

[deepak1556]

Fixes #230200

gulpfile.scan.js was eagerly evaluating the dependency extraction as a side effect of loading the gulpfile via

vscode/build/gulpfile.js

Lines 51 to 53 in 516ecdd

	// Load all the gulpfiles only if running tasks other than the editor tasks
	require('glob').sync('gulpfile.*.js', { cwd: __dirname })
	.forEach(f => require(`./${f}`));

. This interferes with build task when switching branches that could contain possibly different dependency trees. The task is only meant to run in SDL scan CI on demand, so make the relevant calls lazy as well.

/cc @rzhao271