revlog: register changelogv2 C implementation in parsers
This allows Python code to make use of the C implementation of the changelogv2
base operations when the C extensions are enabled.
The `format_version` values are now shared between the C and Python sides,
avoiding an additional translation for the selection of the format version to
use.
Differential Revision: https://phab.mercurial-scm.org/D12179
BasedOnStyle: LLVM
IndentWidth: 8
UseTab: ForIndentation
BreakBeforeBraces: Linux
AllowShortIfStatementsOnASingleLine: false
IndentCaseLabels: false
AllowShortBlocksOnASingleLine: false
AllowShortFunctionsOnASingleLine: false
IncludeCategories:
- Regex: '^<'
Priority: 1
- Regex: '^"'
Priority: 2