This includes a few separate enhancements:
  1. `growable` is added to allow for fixed-size buffers
  2. `ios_t` struct layout is optimized for better packing
  3. inline buffer is increased to 83 bytes from 54

This change grows the size of ios_t by 16 bytes (160 -> 172 bytes), but
the internal buffer was increased by 29 bytes thanks to re-arranging the
fields in the struct to be packed more efficiently.

This adds a variety of metadata to send to Tracy during profiling, in
particular method instance signatures, the Heap size, and a couple of
other small pieces of relevant metadata.

It also adds full support for Task execution, tracking these as "Fibers"
on the Tracy side. This does incur some overhead until an enhancement
is implemented on the Tracy-side to avoid a globally synchronous Fiber
event queue, but most of the events that we're tracking now are
relatively coarse so it should not be a major issue.

This environmental variable instructs the Julia runtime to wait until
it receives a connection from the Tracy profiler before starting.

This allows us to get a complete trace, without having to accumulate a
large queue of events to send over the wire later.

This functionality is currently only exposed on the master branch of
Tracy, but it's quite useful so let's carry the patch to expose it until
the next Tracy release.

This is useful for Tracy, which can receive method signature strings
over the write. For performance reasons, we want to keep those strings
as small as possible, typically less than 80 characters long.

This change adds basic "configuration" support for `jl_static_show`,
including only a "quiet" parameter for now which can be used to avoid
printing DataType parameters.

This replaces the `ENABLE_TIMINGS` #define in `options.h`

Since we now support multiple back-ends for timing events, each back-end
is expected to be enabled with a `WITH_*` Makefile flag, and then the
JL_TIMING API is automatically enabled if any back-end is available.

Turning on multiple back-ends at the same time is also supported.

Cap the number of method instances we report to the profiler for a
single LLVM_MODULE_FINISH to 10.

This enables broadcast messages so that Tracy processes can be listed
by the profiler, which is a nice quality-of-life feature.

This commit adds the following environment variables:
  - `JULIA_TIMING_SUBSYSTEMS` which can be set to, e.g.,
    "+INFERENCE,-GC,METHOD_MATCH" to enable INFERENCE
    and METHOD_MATCH and disable GC.
  - `JULIA_TIMING_METADATA_PRINT_LIMIT` which defaults
    to 10 and determines how many metadata items to add to
    a single timing zone before truncating

This commit also includes other miscellaneous changes to incorporate
review feedback.

We'll eventually want to provide some kind of useful interface to turn
this on for a particular pre-compilation, but for now we should just
prevent causing pre-compilation to hang forever.