filemerge: inline `_filemerge()` into `filemerge()` The caller is now trivial, so the indirection is pointless. Differential Revision: https://phab.mercurial-scm.org/D11860

filemerge: make `_filemerge()` do both premerge and merge This patch removes the `premerge` argument from `_filemerge()` and makes it do both the "premerge" and "merge" steps without the caller having to call it twice. Differential Revision: https://phab.mercurial-scm.org/D11859

filemerge: merge `premerge()` into `filemerge()` Differential Revision: https://phab.mercurial-scm.org/D11858

mergestate: inline `_resolve()` into `resolve()` The caller is now trivial, so the indirection is pointless. Differential Revision: https://phab.mercurial-scm.org/D11857

mergestate: make `_resolve()` do both preresolve and resolve This patch removes the `preresolve` argument from `_resolve()` and makes it do both the "preresolve" and "resolve" steps without the caller having to call it twice. Differential Revision: https://phab.mercurial-scm.org/D11856

mergestate: merge `preresolve()` into `resolve()` The separation between `preresolve()` and `resolve()` was something added for the "merge driver" feature. Since we removed that in 32ce4cbaec4b (mergedriver: delete it, 2020-09-17), we don't need the separation anymore. More cleanups will follow. Differential Revision: https://phab.mercurial-scm.org/D11855

tests: remove unnecessary explicit args from `failfilemerge.py` The `failfilemerge()` function always raises an exception without looking at its arguments, so let's use `*args` and `**kwargs`. Differential Revision: https://phab.mercurial-scm.org/D11854