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GH-39147: [R] Add Bootstrap.r (#39148)

### Rationale for this change
Currently installing via github is not possible because the vendoring of the cpp source isn't happening. We can use bootstrap.R to do it. (Does not work for `devtools::install_local()` as that copies the source folder before running bootstrap.R)
 
### What changes are included in this PR?

An R'ified version of `make sync-cpp`

### Are these changes tested?

locally

### Are there any user-facing changes?
Yes, installing via `devtools::install_github()` will now properly vendor the cpp files.

* Closes: #39147
* GitHub Issue: #39147

Lead-authored-by: Jacob Wujciak-Jens <jacob@wujciak.de>
Co-authored-by: Dewey Dunnington <dewey@dunnington.ca>
Signed-off-by: Jacob Wujciak-Jens <jacob@wujciak.de>