Some tests are running yarn install during the test.
The directory used for isolation test is not subject to yarn workspace,
and it occurs because the required package is not installed.
In order to avoid this, I fixed all necessary packages to be installed
before run test and use symlink to `node_modules`.
This is a bit complicated, as `yarn install` needs to be run in a specific
directory before running the test.
However, running `yarn install` every time run the test is expensive
when testing locally and should be avoided.
* Global ignores at toplevel .gitignore
* Component-specific ignores in each toplevel directory
* Remove `actionview/test/tmp/.keep` for JRuby
```
rm actionview/test/tmp/ -fr
cd actionview/
bundle exec jruby -Itest test/template/digestor_test.rb
```
Related to #11743, #30392.
Closes#29978.
yuuji.yaginuma