Optimize boolean fields in JSFunctionDef, JSParseState and JSToken

[speedskater1610]

Changed multiple boolean fields in JSFunctionDef and JSParseState structures from 'bool' to '_Bool flag : 1' to optimize memory usage while maintaining readability. This is realted to issue #1125.

[akrieger]

bool is just a macro for _Bool until C23 after which _Bool is deprecated and bool is the only correct option, so feels like just sticking with bool is appropriate.

[speedskater1610]

Sorry, I didn't realize; I’ve updated the fields to use bool flag : 1 instead. The intent was mainly to reduce the memory footprint of these structs, since they contain many flags, and bit-field width still provides a measurable space optimization even when keeping bool.

[bnoordhuis]

Changing a field to a bool : 1 is only useful if there's an adjacent field to merge with.

Phrased another way, something like struct S { int x; bool b:1; }; is pointless and potentially a deoptimization:

• pointless because the struct size remains the same (even on ppc, I suspect, because of alignment requirements), and
• a deoptimization if the compiler still emits extra instructions when accessing the field.

That's why I mentioned reordering fields in the linked issue. There are probably also plenty of opportunities to reduce the bit size of adjacent fields; in lots of places we store things like lengths that fit in 31 bits as uint32s. Such changes need to be carefully considered and reviewed though.

I suggest updating this PR to only cover the lowest-hanging fruit like JSFunctionDef, and then follow up with a series of pull requests where you pick off the more complicated ones one by one.

[speedskater1610]

In this commit, all previous bool : 1 changes in other structs were reverted. Only JSFunctionDef was optimized: all boolean flags are now grouped as 1-bit bitfields to reduce struct size and avoid padding.