RFR: 8299162: Refactor shared trampoline emission logic

[Xiaolin Zheng]

After the quick fix [JDK-8297763](https://bugs.openjdk.org/browse/JDK-8297763), shared trampoline logic gets a bit verbose. If we can turn to batch emission of trampoline stubs, pre-calculating the total size, and pre-allocating them, then we can remove the CodeBuffer expansion checks each time and clean up the code around.


[Stub Code]
...
<shared trampoline stub1, (A):>
  align(), emitting nothing or a 4-byte padding
  <..., (B)>    <-- multiple relocations at the pc: __ relocate(<the pc here>, trampoline_stub_Relocation::spec())
  <...>
  <..., (C)>
<shared trampoline stub2:>
  align(), emitting nothing or a 4-byte padding
  <...>        <-- multiple relocations at the pc: __ relocate(<the pc here>, trampoline_stub_Relocation::spec())
  <...>
  <...>
<shared trampoline stub3:>
  align(), emitting nothing or a 4-byte padding
  <...>        <-- multiple relocations at the pc: __ relocate(<the pc here>, trampoline_stub_Relocation::spec())
  <...>
  <...>


Here, the `pc_at_(C) - pc_at_(B)` is the fixed length `NativeCallTrampolineStub::instruction_size`; but the `pc_at_(B) - pc_at_(A)` may be a 0 or 4, which is not a fixed-length value.

So originally:
The logic of the lambda `emit()` inside the `emit_shared_trampolines()` when emitting a shared trampoline:

We are at (A) -> 
do an align() -> 
We are at (B) -> 
emit lots of relocations bound to this shared trampoline at (B) -> 
do an emit_trampoline_stub() -> 
We are at (C)


After this patch:

We are at (A) -> 
do an emit_trampoline_stub(), which contains an align() already ->
We are at (C) directly ->
reversely calculate the (B) address, for `pc_at_(C) - pc_at_(B)` is a fixed-length value -> 
emit lots of relocations bound to this shared trampoline at (B)


Theoretically the same. Just a code refactoring and we can remove some checks inside and make the code clean.

Tested AArch64 hotspot tier1~4 with fastdebug build twice; Tested RISC-V hotspot tier1~4 with fastdebug build on hardware once.


Thanks,
Xiaolin

-------------

Commit messages:
 - Refactor and cleanup for shared trampolines

Changes: https://git.openjdk.org/jdk/pull/11749/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11749&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8299162
  Stats: 104 lines in 9 files changed: 44 ins; 29 del; 31 mod
  Patch: https://git.openjdk.org/jdk/pull/11749.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11749/head:pull/11749

PR: https://git.openjdk.org/jdk/pull/11749