DDC generated code is slow to start up in Safari

[vsmenon]

Initial startup of DDC apps is relatively slow in Safari, particularly for Flutter Web.

The root cause appears to be a perf bug / lack of optimization in Safari's JSC:

https://bugs.webkit.org/show_bug.cgi?id=199866

We may consider working around this in DDC by using var instead of let or const as suggested on the above.

[sigmundch]

How many of these declarations are top-level on the module?

I wonder if this will improve once we land the change to hoist variables, which @Markzipan is looking into in order to improve stepping in the debugger.

[vsmenon]

( @redbrogdon )

I think we can close this one if you prefer. Using var fixed / sidestepped the issue (see the webkit bug).

We could restore let / const at some point, but I don't know if we still need this issue.

[sigmundch]

thanks