Add support for Bicep when installed as a plugin to Azure CLI (#4496)

* Add support for Bicep when installed as a plugin to Azure CLI

The compiler for Microsoft's DSL Bicep can be installed both
independently and as a plugin to Azure CLI. The latter is probably how
most people install it.

The program output is the same but Azure CLI wraps the arguments and has
a slightly different interface, hence I opted to copy the old linter and
modify it to match the plugin arguments.

* Fix bicep/az_bicep tests, arguments and parsing

* Actually test the ale_linters#bicep#az_bicep#Handle function in the
  test that should test that function, not
  ale_linters#bicep#bicep#Handle.

* Use the same method as in bicep/bicep for discarding output file, i.e.
  by specifying --outfile to a null file.

* Fix parsing of occasionally occurring leading error type (such as
  'ERROR: ').

* Correct option defaults for bicep & az_bicep specified in documentation

doc/ale-bicep.txt

@@ -16,9 +16,28 @@ g:ale_bicep_bicep_executable                      *g:ale_bicep_bicep_executable*
 g:ale_bicep_bicep_options                            *g:ale_bicep_bicep_options*
                                                      *b:ale_bicep_bicep_options*
   Type: |String|
-  Default: `'build --outfile /dev/null'`
+  Default: `''`
 
   This variable can be set to pass additional options to bicep.
 
+
+===============================================================================
+az_bicep                                                    *ale-bicep-az_bicep*
+
+g:ale_bicep_az_bicep_executable                *g:ale_bicep_az_bicep_executable*
+                                               *b:ale_bicep_az_bicep_executable*
+  Type: |String|
+  Default: `'az'`
+
+  This variable can be set to change the path to az_bicep.
+
+
+g:ale_bicep_az_bicep_options                      *g:ale_bicep_az_bicep_options*
+                                                  *b:ale_bicep_az_bicep_options*
+  Type: |String|
+  Default: `''`
+
+  This variable can be set to pass additional options to az_bicep.
+
 ===============================================================================
   vim:tw=78:ts=2:sts=2:sw=2:ft=help:norl:

doc/ale.txt

@@ -2858,6 +2858,7 @@ documented in additional help files.
     bibclean..............................|ale-bib-bibclean|
   bicep...................................|ale-bicep-options|
     bicep.................................|ale-bicep-bicep|
+    az_bicep..............................|ale-bicep-az_bicep|
   bitbake.................................|ale-bitbake-options|
     oelint-adv............................|ale-bitbake-oelint_adv|
   c.......................................|ale-c-options|