async/await rewrite follow-up

[andrewrk]

Here are the remaining items that I made note of while working on the async/await branch. Smaller issues can be solved from this list and ticked off. Larger issues will be split into new issues.

• compile error (instead of crashing) for trying to get @Frame of generic function
• compile error (instead of crashing) for trying to async call and passing @Frame of wrong function
• [ ] implicit cast of normal function to async function should be allowed when it is inferred to be async implicit cast of normal function to async function should be allowed when it is inferred to be async #3079
• compile error for error: expected anyframe->T, found 'anyframe'
• compile error for error: expected anyframe->T, found 'i32'
• [ ] peer type resolution of *@Frame(func) and anyframe peer type resolution for *@Frame(func), anyframe->T, and anyframe #3078
• [ ] peer type resolution of *@Frame(func) and anyframe->T when the return type matches peer type resolution for *@Frame(func), anyframe->T, and anyframe #3078
• [ ] for loops need to spill the index. other payload captures probably also need to spill suspensions inside for loops generate invalid LLVM IR #3076
• [ ] const result = (await a) + (await b); this causes "Instruction does not dominate all uses" - need spill using await in an expression generates invalid LLVM IR #3077
• [ ] @typeInfo for @Frame(func) implement @typeInfo for @Frame(func) #3066
• returning a value from within a suspend block
• make resuming inside a suspend block, with nothing after it, a must-tail call.
• make sure there are safety tests for all the new safety features (search the new PanicFnId enum values)
• [ ] compile error for casting a function to a non-async function pointer, but then later it gets inferred to be an async function compile error for casting a function to a non-async function pointer, but then later it gets inferred to be an async function #3075
• [ ] compile error for copying a frame add compile error for copying an async frame #3074
• compile error for resuming a const frame pointer
• runtime safety enabling/disabling scope has to be coordinated across resume/await/calls/return
• calling a generic function which is async
• [ ] make sure await @asyncCall and await async are handled correctly. await @asyncCall and await async should generate the same code as a function call #3065
• [ ] allow @asyncCall with a real @Frame(func) (the point of this is result pointer) allow @asyncCall with a real @Frame(func) rather than byte slice #3072
• [ ] implement @asyncCall with null as the result pointer support @asyncCall with null as the result pointer #3068
• [ ] when there are multiple calls to async functions in a function, reuse the same frame buffer, so that the needed bytes is equal to the largest callee's frame smarter data layout of local variables inside async function frame to save space #3069
• [ ] await should not be a suspend point when used on a @Frame(func) and func is blocking. await should not be a suspend point when used on a @Frame(func) and func is blocking #3067