Move eventpipe buffer to TLS (#21817)

Move eventpipe buffer to TLS (#21817)

* start ripping out eventpipe buffer to tls

* can now emit events from gc threads

* cleanup

* more cleanup

* more cleanup

* tested on linux

* Addressing PR comments

* Move things around a bit to build in Linux

* change eventpipe buffer deallocation code

* more cleanup

* this while loop doesnt do anything now

* Fix build

* fixing build

* More cleanup

* more pr comments

* Fix unix build

* more pr comments

* trying to add a message to assertion that seems to be causing CIs to fail

* more pr feedback

* handle non-2-byte aligned string payloads inside payload buffers

* some more cleanup

* Fix off by one error in null index calculation

* Make Get/SetThreadEventBufferList a static member of ThreadEventBufferList

* make only the methods public in ThreadEventBufferList

* Addressing noah's comments

* fix comment and last off by 1 error