fix: build source maps

[guybedford]

Resolves #2414.

[github-actions]

File size impact

Merging fix-sourcemaps into main will impact 9 files in 2 groups.

browser (1/2)

File	raw	gzip	brotli	Event
dist/system.min.js	0 (12,042)	-2 (4,645)	-6 (4,181)	modified
Total size impact	0 (12,042)	-2 (4,645)	-6 (4,181)

node (0/1)

No impact on files in node group.

extras (8/8)

File	raw	gzip	brotli	Event
dist/extras/amd.min.js	-3 (1,283)	-3 (690)	-4 (592)	modified
dist/extras/dynamic-import-maps.min.js	+13 (350)	+5 (265)	+1 (203)	modified
dist/extras/global.min.js	0 (857)	-3 (505)	+1 (424)	modified
dist/extras/module-types.min.js	+6 (2,819)	0 (1,214)	-6 (1,062)	modified
dist/extras/named-exports.min.js	+7 (673)	+5 (403)	-2 (330)	modified
dist/extras/named-register.min.js	+8 (989)	+1 (461)	-2 (394)	modified
dist/extras/transform.min.js	+3 (667)	-4 (405)	+15 (350)	modified
dist/extras/use-default.min.js	+5 (247)	+1 (201)	-2 (144)	modified
Total size impact	+39 (7,885)	+2 (4,144)	+1 (3,499)

_{Generated by file size impact during size-impact#2882931233}