Add tooltip annotation and replace deprecated obs_properties_add_button

[andilippi]

Summary

Two changes to obs-shaderfilter.c:

• New tooltip annotation on shader uniforms. Writing string tooltip = "..."; inside any uniform's annotation block applies the string via obs_property_set_long_description, so OBS shows the description on hover. Wired through every property type: bool, float, int, vec2, vec3, vec4, texture, string. For vector slider variants (vec2/vec3/vec4 with widget_type = "slider") the tooltip applies to each sub-axis, so hovering X, Y, Z or W all surface the same hint.
• Replaces the deprecated obs_properties_add_button call for the Reload Effect button with obs_properties_add_button2. The old API produces a C4996: was declared deprecated warning that breaks the build under warnings-as-errors against current OBS headers. The other button call in this file (shader_convert) was already on the new API, so this is just one straggler. Behaviour is unchanged: the callback already had the (props, property, data) signature the new API expects, and the data pointer that used to come implicitly through obs_properties_set_param is now passed explicitly in the call.

Usage example

uniform float MySlider <
    string label = "My Slider";
    string tooltip = "Shown on hover in the property panel.";
    string widget_type = "slider";
    float minimum = 0.0;
    float maximum = 1.0;
    float step    = 0.01;
> = 0.5;

Test plan

• Existing example shaders still parse and render their properties correctly
• Adding string tooltip = "..."; to a uniform shows the description on hover
• Vector sliders (vec2/3/4) show the same tooltip on every axis
• Reload Effect button still reloads the effect when clicked
• Build is clean against current OBS headers (no C4996)