shell-init creates ~/.bashrc on macOS, where login bash never reads it

[fcreme]

When tstyles shell-init finds no rc file at all, it creates one for the login
shell rather than silently doing nothing (terminals.ps1, ~line 616):

$loginShell = if ($env:SHELL -and $env:SHELL -match 'zsh') { 'zsh' } else { 'bash' }
$target = $candidates | Where-Object Shell -eq $loginShell | Select-Object -First 1

Get-ShellRcCandidate returns the bash candidates in the order .bashrc,
.bash_profile, so -First 1 always picks .bashrc.

That is the wrong file on macOS, and the reason is documented two functions
away, in Get-ShellRcCandidate's own comment:

~/.bash_profile is included because macOS Terminal.app starts bash as a
LOGIN shell, which reads .bash_profile and never .bashrc.

So on a fresh macOS machine whose login shell is bash and which has no rc files
yet, shell-init creates ~/.bashrc, reports success, and the shell never
reads it.

Expected

Create the file the login shell will actually read — .bash_profile on macOS,
.bashrc on Linux.

Why this is a good first issue

The reasoning is already written down in the file; this is about applying it in
one more place. Get-TStylesPlatform gives you the platform, and
tests/Shell-Integration.Tests.ps1 shows how the rc-file paths are faked.