Cleanup patch_info code a little. (#14037)

Cleanup patch_info code a little. (#14037)

 e.g. whenever underlying representation is nul terminated string.
 MONO_PATCH_INFO_LDSTR_LIT
 MONO_PATCH_INFO_OBJC_SELECTOR_REF
almost the same as
 MONO_PATCH_INFO_JIT_ICALL
 MONO_PATCH_INFO_JIT_ICALL_ADDR
 MONO_PATCH_INFO_JIT_ICALL_ADDR_NOCALL

MONO_PATCH_INFO_LDSTR_LIT no longer allocate
 and copy the string from the AOT image into image_pool.

g_str_equal check pointer equality first.
While obviously correct, not obviously faster,
as it adds cost when strings are unequal.

Uninline g_str_equal, seems cleaner, but perhaps less efficient.

Combine the switch-exit and default: paths,
as only one case other than default exited the switch.

Lift out other common subexpressions.