[REF] web, *: review the assets helpers organization

* survey, website_slides

While not changing their name or their amount, this commit reorganizes
the assets helpers to:

Avoid all file duplicates in different helpers
----------------------------------------------

Before, we had to put some files in different helpers, like our
bootstrap mixin overrides which were in the _assets_utils template and
in the _assets_bootstrap template.

Enforce the use of an helper when using bootstrap
-------------------------------------------------

Bootstrap functions, variables and mixins are now out of the
_assets_bootstrap template, which now only contains bootstrap css rules
and our bootstrap fixes and extensions.

Allow using the correct bootstrap utils in all assets
-----------------------------------------------------

In some assets (especially editor ones), we may want to use bootstrap
variables even though bootstrap is not included in those. This worked
before but using *default* bootstrap variables. Now, our overrides can
be properly included if necessary.

Note: this commit may also be a first step to allow for backend
bootstrap and frontend bootstrap to co-exist.

closes odoo/odoo#28204

2 files changed, 8 insertions, 16 deletions

diff --git a/addons/web/static/src/scss/import_bootstrap_part2.scss b/addons/web/static/src/scss/import_bootstrap.scss
index c15793019ad..d3d033a3575 100644
--- a/addons/web/static/src/scss/import_bootstrap_part2.scss
+++ b/addons/web/static/src/scss/import_bootstrap.scss
@@ -1,11 +1,14 @@
 
 // This file is importing bootstrap. While a simple "import "bootstrap";"
-// should be enough, this does not allow overridding mixins. Overridding mixins
-// is necessary for some of our need and allow to generate more efficient CSS
-// than adding more rules. This file instead copies the second part of the
-// content of the "bootstrap.scss" files to allow adding mixin overrides in
-// between.
+// should be enough, this does not allow overridding mixins/functions.
+// Overridding those is necessary for some of our need and allow to generate
+// more efficient CSS than adding more rules. This file instead copies the
+// content of the "bootstrap.scss" files but do not import functions, variables
+// and mixins which will be handled "by hand" in _assets_helpers.
 
+// @import "functions";
+// @import "variables";
+// @import "mixins";
 @import "root";
 @import "reboot";
 @import "type";
diff --git a/addons/web/static/src/scss/import_bootstrap_part1.scss b/addons/web/static/src/scss/import_bootstrap_part1.scss
deleted file mode 100644
index 09f4d3579ac..00000000000
--- a/addons/web/static/src/scss/import_bootstrap_part1.scss
+++ /dev/null
@@ -1,11 +0,0 @@
-
-// This file is importing bootstrap. While a simple "import "bootstrap";"
-// should be enough, this does not allow overridding mixins. Overridding mixins
-// is necessary for some of our need and allow to generate more efficient CSS
-// than adding more rules. This file instead copies the first part of the
-// content of the "bootstrap.scss" files to allow adding mixin overrides in
-// between.
-
-@import "functions";
-@import "variables";
-@import "mixins";