feat: list and dict literals in tags + fix tag parser

[JuroOravec]

Following up on #872, because, frankly, it was fun to solve 😄

This PR refactors the tag parser, which turns Django's template tag content of e.g.

{% component key=value key2="abc def" / %}

into an AST which can be worked with downstream.

1. This PR fixes the bug in In-template component input that has filter(s) with whitespace don't work #894 - after this PR, it will be possible to have whitespace around filters and translation syntax:

   {% component key=_( "hello" ) key2="abc def" | lower / %}

2. I added support for defining list and dict literals as inputs, and allowing to spread variables into those literal lists and dicts.

   I then took this idea to its logical conclusion, allowing nested lists, dicts, etc. So the syntax works as follows:

   Supported syntax:

   • Variables: val, key
   • Kwargs (attributes): key=val, key2='val2 two'
   • Quoted strings: "my string", 'my string'
   • Translation: _("my string")
   • Filters: val|filter, val|filter:arg
   • List literals: [value1, value2], key=[value1, [1, 2, 3]]
   • Dict literals: {"key1": value1, "key2": value2}, key={"key1": value1, "key2": {"nested": "value"}}
   • Trailing commas: [1, 2, 3,], {"key": "value", "key2": "value2",}
   • Spread operators: ..., *, **
   • Spread inside lists and dicts: key=[1, *val, 3], key={"key": val, **kwargs, "key2": 3}
   • Spread with list and dict literals: {**{"key": val2}, "key": val1}, [ ...[val1], val2 ]
   • Spread list and dict literals as attributes: {% component ...[val1] %}, {% component ...{"key" val1 } %}

   Invalid syntax:

   • Spread inside a filter: val|...filter
   • Spread inside a dictionary key: attr={...attrs: "value"}
   • Spread inside a dictionary value: attr={"key": ...val}
   • Misplaced spread: attr=[...val], attr={...val}, attr=[**val], attr={*val}
   • Spreading lists and dicts: ...[1, 2, 3], ...{"key": "value"}

   This tag content is parsed into an AST that looks like this:

   [
   TagAttr(
       key=None,
       value=TagValueStruct(
           type="simple",
           spread=None,
           meta={},
           entries=[
               TagValue(
                   parts=[
                       TagValuePart(
                           value="component", quoted=None, spread=None, translation=False, filter=None
                       ),
                   ]
               ),
           ],
       ),
       start_index=13,
   )
   ...
   ]

NOTE: I didn't make changes to documentation yet. For one, this is already a huge PR. For second, while I updated the parser, as of this PR, users cannot yet use the literal dicts and lists. Or rather, they can write it, but it will be treated as a string. So I plan to make a second PR to update that part and update documentation with it.

Closes #894

[EmilStenstrom]

This is a nice feature, but with ~3000 lines, it's not worth reviewing imho. I'll just trust the tests in this case :)

[JuroOravec]

Fair point. Just a note, that 2200 lines of that are purely tests, because it's about 30 tests, and the AST takes up a lot of space.