2.0 branch fixes: no LineTooLong, update macos CI (#23184)

Adapts #23108 to the version-2-0 branch and makes the 2.0 compiler
define `nimHasNoLineTooLong` as the devel compiler depends on it to not
turn off `hint[LineTooLong]`, which means the 2.0 compiler errors on the
devel compiler config (as mentioned in
https://github.com/nim-lang/Nim/issues/23178#issuecomment-1880511322).

Would have these as separate PRs but the macos CI PR would have to be
merged first, then the second PR would have to be rebased.

.github/workflows/ci_docs.yml

@@ -47,7 +47,7 @@ jobs:
           - target: windows
             os: windows-2019
           - target: osx
-            os: macos-11
+            os: macos-12
 
     name: ${{ matrix.target }}
     runs-on: ${{ matrix.os }}

.github/workflows/ci_packages.yml

@@ -17,7 +17,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-20.04, macos-11]
+        os: [ubuntu-20.04, macos-12]
         cpu: [amd64]
         batch: ["allowed_failures", "0_3", "1_3", "2_3"] # list of `index_num`
     name: '${{ matrix.os }} (batch: ${{ matrix.batch }})'