RFR: 8348858: [leyden] Bump the default code buffer sizes to store more generated code [v2]

[Aleksey Shipilev]

> Due to current prototype limitation, we cannot yet store the generated code that has the expanded code buffer. I tried to address that directly, but I think relocations disagree with the whole thing, so this implementation limitation stays for a bit longer. I turned the bailout due to that cause from `info` into `warning`.
> 
> On `JavacBenchApp 50`, this causes us to lose 700 (!) C2 compiled methods from the SCC! We can dodge significant part of the hit by bumping the default code buffer sizes, and thus making buffers less likely to require resizing, and thus allowing to store more code in SCC. 
> 
> Additional testing:
>  - [x] Linux x86_64 server fastdebug, `runtime/cds`

Aleksey Shipilev has updated the pull request incrementally with one additional commit since the last revision:

  G1 barrier size estimates are not working well, do the conservative hack for Leyden

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Changes:
  - all: https://git.openjdk.org/leyden/pull/28/files
  - new: https://git.openjdk.org/leyden/pull/28/files/c8f9b347..0fe629c1

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=leyden&pr=28&range=01
 - incr: https://webrevs.openjdk.org/?repo=leyden&pr=28&range=00-01

  Stats: 33 lines in 5 files changed: 9 ins; 20 del; 4 mod
  Patch: https://git.openjdk.org/leyden/pull/28.diff
  Fetch: git fetch https://git.openjdk.org/leyden.git pull/28/head:pull/28

PR: https://git.openjdk.org/leyden/pull/28