Allow using loop variables in ReactiveHTML templates

[philippjfr]

Allows making use of loop variables instead of the more cumbersome indexing syntax, e.g. this:

class Select(ReactiveHTML):

    options = param.List(doc="Options to choose from.")
    
    value = param.String(doc="Current selected option")
    
    _template = """
    <select id="select" value="${value}">
      {% for obj in options %}
      <option id="option-{{ loop.index0 }}">${objects[{{ loop.index0 }}]}</option>
      {% endfor %}
    </select>
    """

Can now be written as:

class Select(ReactiveHTML):

    options = param.List(doc="Options to choose from.")
    
    value = param.String(doc="Current selected option")
    
    _template = """
    <select id="select" value="${value}">
      {% for obj in options %}
      <option id="option">${obj}</option>
      {% endfor %}
    </select>
    """

[codecov]

Codecov Report

Merging #2287 (1631f8b) into master (799132f) will increase coverage by 0.03%.
The diff coverage is 97.01%.

@@            Coverage Diff             @@
##           master    #2287      +/-   ##
==========================================
+ Coverage   83.64%   83.67%   +0.03%     
==========================================
  Files         183      183              
  Lines       21947    22007      +60     
==========================================
+ Hits        18357    18415      +58     
- Misses       3590     3592       +2     

Impacted Files	Coverage Δ
panel/reactive.py	76.34% <91.66%> (+0.19%)	⬆️
panel/models/reactive_html.py	81.81% <96.66%> (+3.00%)	⬆️
panel/tests/test_reactive.py	99.07% <100.00%> (+0.12%)	⬆️

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