tryAdd shouldn't succeed (and accept the new frame) if the last
existing frame on the deck is not an inlined frame.

For example, when we see the followig stack
[300656 300664 300655 300664]

with each PC corresponds to

[{PC:300656 Func:nil Function:runtime.nanotime File:/workdir/go/src/runtime/time_nofake.go Line:19 Entry:300416 {0x28dac8 0x386c80}}]
[{PC:300664 Func:0x28dac8 Function:runtime.checkTimers File:/workdir/go/src/runtime/proc.go Line:2623 Entry:300416 {0x28dac8 0x386c80}}]
[{PC:300655 Func:nil Function:runtime.nanotime File:/workdir/go/src/runtime/time_nofake.go Line:19 Entry:300416 {0x28dac8 0x386c80}}]
[{PC:300664 Func:0x28dac8 Function:runtime.checkTimers File:/workdir/go/src/runtime/proc.go Line:2623 Entry:300416 {0x28dac8 0x386c80}}]

PC:300656 and PC:300664 belong to a single location entry,
but the bug in the current tryAdd logic placed the entire stack into one
location entry.

Also adds tests - this crash is a tricky case to test because I think it
should happen with normal go code. The new TestTryAdd simulates it by
using fake call sequences. The test crashed without the fix.

Update #35538

Change-Id: I6d3483f757abf4c429ab91616e4def90832fc04a
Reviewed-on: https://go-review.googlesource.com/c/go/+/206958Reviewed-by: Keith Randall <khr@golang.org>