Use form native compilation in `comp-trampoline-compile'

Use form native compilation in `comp-trampoline-compile'

	* lisp/emacs-lisp/comp.el (comp-trampoline-sym): Remove function.
	(comp-trampoline-filename): As we are introducing an ABI change in
	the eln trampoline format change the trampoline filename to
	disambiguate.
	(comp-trampoline-search): Rename from `comp-search-trampoline'
	and return directly the trampoline.
	(comp-trampoline-compile): Rework to use native form compilation
	in place of un-evaluating a function and return directly the
	trampoline.
	(comp-subr-trampoline-install): Update for
	`comp-trampoline-search' and `comp-trampoline-compile' new
	interfaces.
	* src/comp.c (Fcomp__install_trampoline): Store the trampoline
	itself as value in `comp-installed-trampolines-h'.
	(syms_of_comp): Doc update `comp-installed-trampolines-h'.