transition typesem.d to eSink

[WalterBright]

Despite all the diffs, this is an easy review, because it's the same thing over and over.

[github-actions]

DMD perf check

Metric	Base	PR	delta
compile hello.d (instr)	215.9 M	215.9 M	+0.03%
compile hello.d -O (instr)	234.4 M	234.5 M	+0.03%
compile Phobos (instr)	5,125.5 M	5,131.5 M	+0.12%
compile Phobos codegen (instr)	1,472.2 M	1,472.5 M	+0.02%
compile vibe.d (instr)	15,127.0 M	15,137.2 M	+0.07%
dmd binary size (stripped)	6.94 MB	6.94 MB	+0.06%
hello binary size	0.72 MB	0.72 MB	0.00%
peak RSS (compile hello.d)	43 MB	43 MB	+0.14%
peak RSS (compile Phobos)	618 MB	619 MB	+0.21%
peak RSS (compile vibe.d)	1916 MB	1917 MB	+0.02%